set up simplecov

I had to change a bunch of `require`s to `require_relative` to resolve
pathing issues when running this. You can run the coverage with
`ruby test/test_all_basic.rb`, then open up `coverage/index.html`
Merge pull request #147 from mockdeep/simplecov

Add SimpleCov
Let 1.8 fail
Merge pull request #155 from gemhome/let_it_fail

Let 1.8 fail
Break extconf.rb into an object with methods
Make extconf.rb 1.8 compatible