man/dockerd.8: escape asterisks and underscores

1. Escape asterisks and underscores, that have special meaning in
   Markdown. While most markdown processors are smart enough to
   distinguish whether it's a literal * or _ or a formatting directive,
   escaping makes things more explicit.

2. Fix using wrong level of headings in some dm options (most are ####,
   but some were #####).

3. Do not use sub-heading for examples in some dm options (this is how
   it's done in the rest of the man page).

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

man/dockerd.8.md

@@ -137,7 +137,7 @@ $ sudo dockerd --add-runtime runc=runc --add-runtime custom=/usr/local/bin/my-ru
 
 **--api-cors-header**=""
   Set CORS headers in the Engine API. Default is cors disabled. Give urls like
-  "http://foo, http://bar, ...". Give "*" to allow all.
+  "http://foo, http://bar, ...". Give "\*" to allow all.
 
 **--authorization-plugin**=""
   Set authorization plugins to load
@@ -175,7 +175,7 @@ $ sudo dockerd --add-runtime runc=runc --add-runtime custom=/usr/local/bin/my-ru
 
 **--default-gateway**=""
   IPv4 address of the container default gateway; this address must be part of
-  the bridge subnet (which is defined by \-b or \--bip)
+  the bridge subnet (which is defined by \-b or \-\-bip)
 
 **--default-gateway-v6**=""
   IPv6 address of the container default gateway
@@ -231,7 +231,7 @@ $ sudo dockerd --add-runtime runc=runc --add-runtime custom=/usr/local/bin/my-ru
 **-H**, **--host**=[*unix:///var/run/docker.sock*]: tcp://[host:port] to bind or
 unix://[/path/to/socket] to use.
   The socket(s) to bind to in daemon mode specified using one or more
-  tcp://host:port, unix:///path/to/socket, fd://* or fd://socketfd.
+  tcp://host:port, unix:///path/to/socket, fd://\* or fd://socketfd.
 
 **--help**
   Print usage statement
@@ -463,7 +463,7 @@ Example use:
    $ dockerd \
          --storage-opt dm.thinpooldev=/dev/mapper/thin-pool
 
-#### dm.directlvm_device
+#### dm.directlvm\_device
 
 As an alternative to manually creating a thin pool as above, Docker can
 automatically configure a block device for you.
@@ -473,40 +473,40 @@ Example use:
    $ dockerd \
          --storage-opt dm.directlvm_device=/dev/xvdf
 
-##### dm.thinp_percent
+#### dm.thinp\_percent
 
 Sets the percentage of passed in block device to use for storage.
 
-###### Example:
+Example:
 
    $ sudo dockerd \
         --storage-opt dm.thinp_percent=95
 
-##### `dm.thinp_metapercent`
+#### dm.thinp\_metapercent
 
 Sets the percentage of the passed in block device to use for metadata storage.
 
-###### Example:
+Example:
 
    $ sudo dockerd \
          --storage-opt dm.thinp_metapercent=1
 
-##### dm.thinp_autoextend_threshold
+#### dm.thinp\_autoextend\_threshold
 
 Sets the value of the percentage of space used before `lvm` attempts to
 autoextend the available space [100 = disabled]
 
-###### Example:
+Example:
 
    $ sudo dockerd \
          --storage-opt dm.thinp_autoextend_threshold=80
 
-##### dm.thinp_autoextend_percent
+#### dm.thinp\_autoextend\_percent
 
 Sets the value percentage value to increase the thin pool by when `lvm`
 attempts to autoextend the available space [100 = disabled]
 
-###### Example:
+Example:
 
    $ sudo dockerd \
          --storage-opt dm.thinp_autoextend_percent=20
@@ -559,7 +559,7 @@ Specifies extra mount options used when mounting the thin devices.
 
 Example use: `dockerd --storage-opt dm.mountopt=nodiscard`
 
-#### dm.use_deferred_removal
+#### dm.use\_deferred\_removal
 
 Enables use of deferred device removal if `libdm` and the kernel driver
 support the mechanism.
@@ -577,7 +577,7 @@ busy device.
 
 Example use: `dockerd --storage-opt dm.use_deferred_removal=true`
 
-#### dm.use_deferred_deletion
+#### dm.use\_deferred\_deletion
 
 Enables use of deferred device deletion for thin pool devices. By default,
 thin pool device deletion is synchronous. Before a container is deleted, the
@@ -656,7 +656,7 @@ returned to the system for other use when containers are removed.
 
 Example use: `dockerd --storage-opt dm.blkdiscard=false`
 
-#### dm.override_udev_sync_check
+#### dm.override\_udev\_sync\_check
 
 By default, the devicemapper backend attempts to synchronize with the `udev`
 device manager for the Linux kernel.  This option allows disabling that
@@ -692,7 +692,7 @@ support synchronizing with `udev`. For further discussion on this topic, see
 Otherwise, set this flag for migrating existing Docker daemons to a daemon with
 a supported environment.
 
-#### dm.min_free_space
+#### dm.min\_free\_space
 
 Specifies the min free space percent in a thin pool require for new device
 creation to succeed. This check applies to both free data space as well
@@ -717,7 +717,7 @@ the issue.
 
 Example use:: `dockerd --storage-opt dm.min_free_space=10%`
 
-#### dm.xfs_nospace_max_retries
+#### dm.xfs\_nospace\_max\_retries
 
 Specifies the maximum number of retries XFS should attempt to complete IO when
 ENOSPC (no space) error is returned by underlying storage device.
@@ -731,7 +731,7 @@ Example use:
 
     $ sudo dockerd --storage-opt dm.xfs_nospace_max_retries=0
 
-##### dm.libdm_log_level
+##### dm.libdm\_log\_level
 
 Specifies the maxmimum libdm log level that will be forwarded to the dockerd
 log (as specified by --log-level). This option is primarily intended for
@@ -743,13 +743,13 @@ time of writing, the following is the list of libdm log levels as well as their
 corresponding levels when output by dockerd.
 
 | libdm Level   | Value | --log-level |
-| ----------- | -----:| ----------- |
-| _LOG_FATAL  |     2 | error       |
-| _LOG_ERR    |     3 | error       |
-| _LOG_WARN   |     4 | warn        |
-| _LOG_NOTICE |     5 | info        |
-| _LOG_INFO   |     6 | info        |
-| _LOG_DEBUG  |     7 | debug       |
+| ------------- | -----:| ----------- |
+| \_LOG\_FATAL  |     2 | error       |
+| \_LOG\_ERR    |     3 | error       |
+| \_LOG\_WARN   |     4 | warn        |
+| \_LOG\_NOTICE |     5 | info        |
+| \_LOG\_INFO   |     6 | info        |
+| \_LOG\_DEBUG  |     7 | debug       |
 
 Example use:
 
@@ -769,7 +769,7 @@ Example use: `dockerd -s zfs --storage-opt zfs.fsname=zroot/docker`
 
 ## Btrfs options
 
-#### btrfs.min_space
+#### btrfs.min\_space
 
 Specifies the minimum size to use when creating the subvolume which is used for
 containers. If user uses disk quota for btrfs when creating or running a