Better documentation

[smellsblue]

This PR makes the following changes:

• Refactor docs a bit, in particular, break out the reference into separate documents per command
• Embed docs in the gem, and use man to output the docs when gemstash help is run, and embedded txt files when man is unavailable
• Use pandoc to generate all docs from a single source (it generates the new embedded docs, the github markdown docs, and the soon to come html docs)
• Drop the table of contents Rake task, since the new docs structure doesn't need it anymore
• Auto generate the docs when building the gem
• Reduce contents of the built gem to just the lib, and exe dirs, the license, changlog, and code of conduct

This fixes #96

[indirect]

Prettttttty great. 👍 from me!