Traits 4.6.0

This is an incremental release over 4.5, accumulating over a year's worth of
bugfixes and small improvements to the code.

Highlights of this release include:

• support for Python 3.4 and 3.5.
• new Bytes and ValidatedTuple traits.
• a new ArrayOrNone trait which correctly handles None comparisons with Numpy
  arrays.
• clean-up of the ETSConfig code for TraitsUI toolkit selection.
• better compatibility with NumPy scalar types.
• many other bugfixes and improvements.