Add metasploit-yard

MSP-11354
Add rake yard to travis-ci build

MSP-11354
Add Inch CI badge

MSP-11354
Add missing dependency

MSP-11354

metasploit-yard should have declared redcarpet as a dependency, but it
didn't so add it as a development dependency for metasploit-version for
now.
Default yardopts

MSP-11354
Add missing docs

MSP-11354
Update version for branch

MSP-11354
Remove unnecessary `root`

MSP-11354

Root of gems can be derived using Gem::Specification.
Remove obsolete Metasploit::Version::Full from README

MSP-11354

Add in full and gem implementations and update docs to use `(see <method>)`
instead of `@see <method>`, which meant fully-qualifying constants in
full and gem so that the links worked when used on GEM_VERSION and
VERSION.
Use kramdown for jruby

MSP-11354

redcarpet is a cext, so not supported on JRuby.
rake yard for jruby

MSP-11354
Bump MINOR for root removal

MSP-11354

The removal of `Metasploit::Version.root` makes this an incompatible
pre-1.0.0 change, so MINOR is incremented and PATCH is reset.
Fix typo in .travis.yml

MSP-11354
Merge gitignore conflict
Merge pull request #2 from rapid7/feature/MSP-11354/metasploit-yard

Use metasploit-yard