replace shoulda with minitest + add colors + make each file runnable

Conflicts:
	Gemfile.lock
	Rakefile
	business_time.gemspec
	test/helper.rb
	test/test_business_days.rb
	test/test_business_days_eastern.rb
	test/test_business_days_utc.rb
	test/test_time_extensions.rb
	test/test_time_with_zone_extensions.rb
Merge pull request #58 from grosser/grosser/tests

replace shoulda with minitest + add colors + make each file runnable