Add support for standard Go initialisms to avrogo

[ojcm]

Fixes #126

This PR adds support for generating idiomatic names with avrogo.

There is no change in behavior unless new flags are used:

• -goinitialisms turns on the new behaviour using the standard set of Go initialisms
• -extrainitialisms is an optional comma separated list of extra Go initialisms

Note to reviewers: The style/structure of this repo is different to what I'm familiar with. Please let me know if anything is not following the existing conventions and I will update.