Begin process of deprecating MAINTAINER

This may take some time, but start by pointing people at
LABEL instead.

MAINTAINER predates general LABEL and has basically no tooling,
only allows a single item to be added, and is has been
unofficially deprecated for some time, with many images not
including it, but we have never specifically said that it
should be replaced by LABEL as a better more generic metadata
solution.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

docs/deprecated.md

@@ -196,3 +196,7 @@ Since 1.9, Docker Content Trust Offline key has been renamed to Root key and the
 - DOCKER_CONTENT_TRUST_OFFLINE_PASSPHRASE is now named DOCKER_CONTENT_TRUST_ROOT_PASSPHRASE
 - DOCKER_CONTENT_TRUST_TAGGING_PASSPHRASE is now named DOCKER_CONTENT_TRUST_REPOSITORY_PASSPHRASE
 
+### `MAINTAINER` in Dockerfile
+**Deprecated In Release: v1.13.0**
+
+`MAINTAINER` was an early very limited form of `LABEL` which should be used instead.

docs/reference/builder.md

@@ -486,13 +486,6 @@ before each new `FROM` command.
 assumes a `latest` by default. The builder returns an error if it cannot match
 the `tag` value.
 
-## MAINTAINER
-
-    MAINTAINER <name>
-
-The `MAINTAINER` instruction allows you to set the *Author* field of the
-generated images.
-
 ## RUN
 
 RUN has 2 forms:
@@ -687,6 +680,20 @@ To view an image's labels, use the `docker inspect` command.
         "other": "value3"
     },
 
+## MAINTAINER (deprecated)
+
+    MAINTAINER <name>
+
+The `MAINTAINER` instruction sets the *Author* field of the generated images. 
+The `LABEL` instruction is a much more flexible version of this and you should use
+it instead, as it enables setting any metadata you require, and can be viewed
+easily, for example with `docker inspect`. To set a label corresponding to the
+`MAINTAINER` field you could use:
+
+    LABEL maintainer "SvenDowideit@home.org.au"
+
+This will then be visible from `docker inspect` with the other labels.
+
 ## EXPOSE
 
     EXPOSE <port> [<port>...]
@@ -1676,8 +1683,6 @@ something more realistic, take a look at the list of [Dockerization examples](..
 # VERSION               0.0.1
 
 FROM      ubuntu
-MAINTAINER Victor Vieux <victor@docker.com>
-
 LABEL Description="This image is used to start the foobar executable" Vendor="ACME Products" Version="1.0"
 RUN apt-get update && apt-get install -y inotify-tools nginx apache2 openssh-server
 ```