Added the type-class for euclidean domain and the data-type for its fraction field
Added missing exports
added accessors for numerator and denominator
added missing declaration for negate and -
added instance for IntegralSemiring
added Commutative instance
Euclidean
added Characteristic instance
implemented Chinese Remainder Algorithm
Merge branch 'euclidean' of github.com:ekmett/algebra
merge cleanup, style match