Expand mbuild internal help documentation

[Gary Dixon]

Internal help documentation for the mbuild subsystem needs to be expanded in several different ways. Current documentation covers the following topics:

• User interface for the mbuild command (and its supporting commands like mbuild_type).
• Documentation of the statements supported in the Build_script Changes -- section. These statements describe exact contents of an mbuild change_set.
• Documentation for each mbuild request.

Topics missing from the current documentation set include the following.

1. Description of mbuild features, and the special terminology it uses (a glossary of mbuild terms).
2. A list of information blocks available to the mbuild help (h) request (a list_help style overview).
3. A list of supporting compilers, archiving and bind tools, library description tools and other tools known to, and used by the mbuild subsystem.
4. A description of the possible build/install outcomes that can be provided by mbuild, with details for build_directory setup to achieve each of those outcomes.

This ticket proposes that mbuild be enhanced to provide such missing documentation.