v2.0.0

This release primarily enables the <nullable> attribute within the EasyMonads project. As such, I've added and updated several methods to accept nullable reference types. These added and updated methods should eliminate some warnings from consuming projects which also have the <nullable> attribute enabled.

Note, the internal behavior of both the Either and Maybe types has not changed. If a null value is provided to either type, those types will be set to their default states; Neither and None, respectively.

And to be absolutely clear, this does not add support for encapsulating nullable types, such that Maybe<int?> or Either<Unit, string?> could return null values.