Remove simplecov

simplecov 0.9 dropped ruby 1.8 support, and stdlib is one of the oddball
modules that uses it. So we could probably just remove it and be okay.
Merge pull request #308 from hunner/remove_cov

Remove simplecov
Update spec_helper for more consistency
Merge pull request #313 from mhaskel/spec_updates

Update spec_helper for more consistency