Pvax.Functional

Provides following types:
* A set of OneOf types that allow to return one of several type instances;
* Result<TResult, TError> type that allows you to return either method result or error;
* Option<T> type that allows to return either a result or None value instead of null;
* Null class that gives a set of empty method delegates
* InformalProtocl class that gives .Net ability to use Objective-C like informal protocol;
* IErrorInfo interface designed after COM interface with the same name;
and some other useful data types.