Move shared Rake code into the library

This is ugly, but a good temporary way to allow multiple gems to share
this code for now.
Extract Spinach support to another gem
Extract Cucumber support to another gem
Extract RSpec support to another gem
Extract Minitest support to another gem
Extract Test::Unit support to another gem
Remove hoe and switch to bundler-provided builds
Consolidate and update the copyright notice
Remove trailing whitespace
Bump version for a 2.0 alpha
No reason to not test all the branches
Remove support for the "stub" Rakefile
Move RSpec-specific documentation to the RSpec gem
Rewrite README
Merge pull request #130 from shepmaster/split-into-gems

Split into gems