Mark comments that should not be in the docs

Some comments that are meant to separate blocks of code in a file show up
on http://api.rubyonrails.org as though they were part of the documentation.

This commit hides those comments from the documentation.

Stems from the discussion with @zzak at https://github.com/voloko/sdoc/issues/79#issuecomment-64158738

[ci skip]
Merge pull request #17748 from claudiob/remove-unwanted-comments-from-documentation

Mark comments that should not be in the docs [ci skip]