Improve Documentation of add_meta_box()

[philiparthurmoore]

The DocBlocks for add_meta_box do not mention side as an acceptable $context value; ​​Codex does. The attached patch fixes this discrepancy.

[DrewAPicture]

Might as well fix the rest of the phpdoc while we're in there. This is done in 26698.diff​

[nacin]

The only weird thing about this is that these contexts are specified by the particular screen. They are arbitrary. Some pages that implement meta boxes won't have "advanced" and some won't have "side". Not sure what do here, but perhaps it could be made clear hat those are for the post edit screen. We could even spell out the comments screen (normal/side I think) which is the only other core screen (except the dashboard) that uses meta boxes, I think.

[DrewAPicture]

Example contexts

[DrewAPicture]

26698.2.diff​ incorporates the $context description feedback from @nacin in comment:3. I think that should be enough.

[nacin]

In 27132:

Improve parameter documentation of add_meta_box().

props philiparthurmoore, DrewAPicture.
fixes #26698.