Move Yabar documentation to AsciiDoc

[jacksgt]

I moved the Yabar documentation to AsciiDoc format. This has multiple advantages:

• single point of documentation
• auto generated man pages
• online readable (GitHub automatically renders AsciiDoc pages)
• plain-text readable

The documentation is also automatically built by Travis which will prevent any syntax errors from sneaking. While I was at it, I also refactored the Travis job into a build matrix (building yabar and generating the documentation run in parallel).

Please review the correctness of the documentation as-is.

[jacksgt]

@NBonaparte I'm not a fan of huge monolithic commits. IMO commits should be small and logically separate (i.e. the travis change is independent of the the doc change). Just my two cents.