`md5`, `sha1`, `sha256` all take a hexdigest string, e.g:
sha1 'f645e9da45a621415a07a7492c45923b1a1fd4d4'
`no_checksum` takes no argument, and indicates there is no checksum
for this cask. This is *not recommended*, and should only be used for
casks that have no versioned downloads.
`brew cask install` will complain if there is no sum provided (unless
`no_checksum` has been invoked), or if the sums do not match. It will
provide the computed checksum so the cask can be easily amended.
Adapted from @passcod's work in 82cc199ae6bbb1e98950e71a0573ab48e6a641ee
Jumpcut is a tgz file whose handling isn't currently supported.
This commit adds support for it.
The test for tar.gz and tar.bz are very similar and could probably
be refactored. Leaving that as an exercise for another time.
Should have more use cases before opening that up.
