Add p5-MouseX-NativeTraits.

While Mouse attributes provide a way to name your accessors, readers,
writers, clearers and predicates, MouseX::NativeTraits provides
commonly used attribute helper methods for more specific types of
data.

As seen in the "SYNOPSIS", you specify the data structure via the
traits parameter. These traits will be loaded automatically, so you
need not load MouseX::NativeTraits explicitly.

This extension is compatible with Moose native traits, although it
is not a part of Mouse core.

(schmonz)