.NET Standard support, IComparable, test improvements

• Merged PRs #9, #10, #11, #12.

Added rational approximation of floating point types

double, float and decimal can now be converted to rational numbers through explicit conversion, can be parsed as strings, and also converted using the Approximate function.

This function allows for specifying tolerance, increasing tolerance will lead to simpler fractions (e.g. 4/3 instead of 1333/100 when converting 1.333)

Fixed nuget target

1.1.1

Continued fractions

Added support for expanding rational numbers to continued fractions (sequence of coefficients) and constructing rational numbers from continued fractions.

Published on NuGet

1.0.0

Fixed .nuspec file.