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.
add new CurlPostDownloadStrategy

- lib/cask/url.rb: initialize(): add new `:data` attribute to hold post parameters
- lib/cask/download.rb: perform(): dispatch to new class based on `:using => :post`
- lib/cask/download_strategy.rb: Cask::CurlPostDownloadStrategy:
  			extend curl_args with x-www-form-urlencoded data
- doc/CASK_LANGUAGE_REFERENCE.md: HTTP URLs: document new strategy
- test/cask/test_download_strategy.rb: Cask::CurlPostDownloadStrategy: test new strategy
devscripts: prefer GNU xargs

Apple-supplied xargs has bugs/limitations, especially
relevant to the -I flag
add Cask gambit-c.rb
Add uninstall stanza for Logitech Unifying
Update Julia to 0.2.1
Cask for Programmer Dvorak Keyboard layout.
Fixed Java linking path
The Brain 8.0.0.7
Rocks'n'Diamonds 3.3.1.2
instead 2.0.3
Add binary link to kdiff3

Make it accessible via CLI.
jitsi 2.2 -> 2.4
Add uninstall stanza for MacPorts
Update kext-wizard.rb

change the download url
Add uninstall stanza for pandoc
Merge pull request #3465 from alebcay/logitech-unifying

Add uninstall stanza for Logitech Unifying
Merge pull request #3466 from ndr-qef/julia

Update Julia to 0.2.1
Merge pull request #3472 from indeyets/thebrain

The Brain 8.0.0.7
Merge pull request #3473 from indeyets/rocks-n-diamonds

Rocks'n'Diamonds 3.3.1.2