Switch to RSpec

Also install Mutant. Let's get ready to mutate!
Use SimpleCov

Also, add some tests for extra coverage
Remove unnecessary manual cleanup

Since we now wrap tests in transactions that are always rolled back, we
don't need to litter tests with calls to `destroy`.
Increase coverage and quality of GravityForms tests
Better coverage for terms tests
Better spec coverage for config file parsing
"Extract module" refactoring of config code
Further specs for WPDB's initialization code
Extract Method refactoring on WPDB.from_config

This extracts the config file to config object mapper into its own
method for testability and cleanness.
Merge pull request #15 from robmiller/rspec-mutant

Better test coverage