Extract separate shoes-highlighter gem

Update the help system to use the new location.
Necessary gemspec to build shoe-highlighter
Bundler support required by new file structure

Previously our separate 'gems' have worked fine from source simply
because they're all in the lib folder together. Changing that to be
split into separate gem directories actually breaks things unless we get
Bundler into the mix to get our proper load paths set.
LICENSE and README tweaks for new gem
In development use by path, not gemspec

Travis didn't seem happy with it by gemspec and tried to install from Rubygems.
Fix for using shoes-highlighter by path

Was the relative pathing in gemspec that was problematic
Revising version number on shoes-highlighter

Will eventually be independent from main Shoes, so treat it as such.
More common way to reference local gem by path
Farewell, ruby-shoes!

With our new gem structure, bin/ruby-shoes is no longer supported.

bin/shoes-swt is the replacement, and has the necessary code to work
with the changes we're making to gem layout. Additional backends in the
future will be responsible for adding their own executables as well.
Merge pull request #937 from shoes/shoes-highlighter

Introduce shoes-highlighter gem

Fixes #257 and #934

Changelog: feature