Some improvements

[stefan-baumann]

I did some changes which should improve the library a bit:

• I added quite a lot of operators - mainly for equality-checking (Equals(object), Equals(T), ==, !=) but also GetHashCode & ToString
• I removed the LatexString-property which was present in some types and replaced it with a ToLatexString()-Method
• I removed all the custom enumerator classes and replaced them with a much simpler yield-construct to generally simplify the architecture
• I added XML documentation to some classes
• I fixed the FloatingNumberExtension methods (some of them did not work properly as extensions) and renamed them to a (in my opinion) more appropriate name
• I removed unnecessary assembly references which could be a problem when compiling with Mono