Modernize gem structure to fix warnings on 2.0
Fix floating point inprecision
Fix irrelevant inequality parameter order on 2.0

In Ruby 2.0 `coerce` will never be called via method_missing like in 1.9, which
made the ordering of parameters in inequality operations irrelevant in 1.9. To
regain this functionality in 2.0, coerce is defined explicitly.
Merge pull request #100 from Shopify/ruby-2.0.0

Ruby 2.0.0 support