v0.3.0

Added new methods to Option and Result.

Option:

• flatMap - returns None or calls f with the wrapped value and returns Some(f(value));
• filter - returns None if the option is None or predicate returns false, otherwise returns Some.

Result:

• flatMap - calls f if the result is Ok, otherwise returns the Err value of self;
• flatMapErr - Calls f if the result is Err, otherwise returns the Ok value of self.

Full Changelog: v0.2.1...v0.3.0