Implemented basic structure; setup gemspec
Implemented basic gem structure and added required dependencies to the
gemspec except for exerb-mingw. Still working on a way to check for that.
Rake task perhaps?

Added rake tasks:
   test                run tests
   build:clean         clean out artifacts from folder
   build:clobber       clobber the generated binary; called from clean
   build:compile       compiles the current source into a PE binary
   build:install       installs the binary to the specified location (e.g.
                       build:install['C:\Some\Path\Here']

Added rspec for tests and init'd the project.

rbvers commands are added, one command/command group per file with the
file name conforming to `[name]_command.rb` (e.g. version_command.rb) in
the `lib/rbenv/commands` dir. More on this later.