Update primes.rb library with more accurate naming

Also update documentation as per Tomdoc 1.0.0-rc1
Initial Solution for Problem 12

Takes too long to run (>5 minutes on a Core i7).
Bugfix

Assignment of dynamic variables to constants not allowed
Code Cleanup
Code Cleanup
Add tests for primes library
Merge branch 'master' of github.com:eric-hu/Project-Euler