Make caveats a first-class member of the Cask DSL. It no longer has to
be specified with "def caveats", but can be given as "caveats do ... end"
as with after_install blocks.
In addition, create a mini-DSL which can be used within caveats blocks,
providing standard messages when manual installers must be used,
reboot-required, etc.
Add alternate form: caveats can also accept a compile-time string for
simple cases.
This is 99% compatible with old Casks, as it still works by defining
a caveats method. However, all Casks containing caveats are cleaned
up and adapted according to the new DSL.
Full docs in CONTRIBUTING.md.
`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 82cc199ae6
Roland Walker