completion for cask

import from github.com/cask/cask, discussed in PR cask/cask#244
cask: conform to style guide

* no line longer than 79 characters
* indent with 2 spaces
* no capitals in description
update cask subcommands
Add instructions for antigen
Merge pull request #264 from duthils/cask

completion for cask
add hledger completion
Merge pull request #267 from ohcibi/master

Add projects to list of suggestions when tabbing `mux` with no params
Merge pull request #265 from unixorn/add-antigen-instructions

Add instructions for antigen