devscript: add `cask_namer`

This script implements naming rules for App-based Casks
as currently documented.  After some real-world testing, this
logic should be merged into `brew cask create`.  This commit adds
`doc/CASK_NAMING_REFERENCE.md`, and reduces `CONTRIBUTING.md` by
422 words.
Merge pull request #3443 from rolandwalker/cask_namer

devscript: add `cask_namer`