Updated to .NET 6

Added net5 and netstandard2.0 targets and bumped version to 1.3.2

Added strong name for MaybeSharp assembly

Added default parameter values to IMaybe implementations

- while strictly speaking not necessary, they make it more clear to read

Multi-targeting .NET 4.6 and .NET Core

Proper handling of GetHashCode and Equals

Improved API and documentation

Initial release