* convert existing Cask:: namespace to Hbc::
* move Homebrew-fork code under Hbc::
* move freestanding classes such as Tty and TopologicalHash under Hbc::
* recast HOMEBREW_CASK_ constants as HBC_
* modify our Homebrew Formula for backward compatibility
* devscripts and dev docs
* was already done, but inconsistently
* this style follows homebrew Formula
* covers user-facing messages, test titles, comments
* some related minor orthography is included, such
as the consistent spelling of our project name as
"homebrew-cask"
* grammar nits
Replacing `link` for almost all cases.
The `link` stanza can still appear in error messages, because
under the hood, `app` is still implemented as a pure synonym
for the `link` artifact. That will change automatically when
we factor into separate artifacts.
