Use the documentation format for rspec's output
Don't use "should" in test titles
Simplify Enumerable#occurences and Math.primes
Travis: Don't test on JRuby or Rubinius
Refactor a few methods
Use divisible? within magician's own implementations
Use a boolean operator instead of the ternary operator
Add a todo comment
Add Enumerable#none?
Test on Ruby 2.1
Don't test on Rubinius
Merge branch 'develop'

Conflicts:
	.travis.yml
Merge branch 'master' into complex-numbers-for-quadratic