Create a help system

[OrangeTide]

Enhance the "help" command to access a help system.

Requirements for bug closure:

• short write-up of how the help system works, in a README.md or ARCH.md
• one or more help file(s) in the database
• a high-level API for reading and listing help files in the database. (help.c)
• enhance command_do_help() to access the help files

[OrangeTide]

Basic help system added with commit 7be6589f32ff4ab0e873980922e78d5580908c35