Adding dependency for SimpleCov.
Make it so you can run 'rspec' without having to do 'rake rspec'.

... also, tests don't need to include 'require "spec_helper"' anymore.
Add SimpleCov, as an opt-in feature.
Tidy up some no-longer-needed cruft.
Merge pull request #1271 from MrJoy/add_coverage_analysis

Add coverage analysis