API: Add a method to check if a semantic type implements a trait

[xFrednet]

This method could look similar to Clippy's implements_trait util.

Once #93 is resolved, we should have access to the TyDefId of traits. Semantic paths are also almost done (#139). This function will require an option to have the user specify generic arguments for the trait.

In short: This will be fun or at least complex, but the base for this should be set with the two linked issued.

[xFrednet]

Not sure, if I'll be able to complete this for v0.2.0, but I've added it to the tracker for now :)