(maint) Change post_compile_hook method name

Based on discussions around the solution for ticket #3946, it seems
having '_hook' to identify a method's purpose is undesirable. The
desired method of indicating a method's purpose is to use proper YARD
tags.

This commit removes the '_hook' extension.
(doc) Add YARD tags to Puppet::Parameter#post_compile

This commit adds an @api and @since tag to the comments for the
Puppet::Parameter#post_compile method.
Merge pull request #1921 from trlinkin/post_compile_maint

(maint) Change post_compile_hook method name