Handle common RDoc::Markup tasks for various CodeObjects
This module is loaded by generators.  It allows RDoc's CodeObject tree
to avoid loading generator code to improve startup time for
ri.
Namespace
    - MODULE RDoc
 - MODULE RDoc::Generator
 - MODULE RDoc::Generator::Markup
 - CLASS RDoc::ClassModule
 - CLASS RDoc::CodeObject
 - CLASS RDoc::Context
 - CLASS RDoc::Context::Section
 - CLASS RDoc::MethodAttr
 - CLASS RDoc::TopLevel