Proteus and the Raise of the Gogo Options

This includes the following features and fixes:

• Proteus now detects a String method and add the option to drop the generated one
  if it finds it.
• Fixes the mapping for time.Duration.
• Fixes the problems caused by calling proteus twice.
• Fixes the generation of getters by default. This option was early on in the
  development but somehow it got lost.