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
Cask for Programmer Dvorak Keyboard layout.
Fixed Java linking path
update plex-media-server to 0.9.9
Merge pull request #3487 from jimbojsb/pms-0.9.9

update plex-media-server to 0.9.9
Added new cask for Scroll Reverser v1.6
Add Axureprpro v7.0
Fix picasa sha256 sum check dismatch
DeltaWalker 2.0.1
Merge pull request #3468 from sigito/patch-1

Fixed Java linking path
safer uninstall for iphone-configuration-utility

per discussion in #3434 .
Merge pull request #3457 from rolandwalker/iphone_config_uninstall

safer uninstall for iphone-configuration-utility
Merge pull request #3491 from ahbeng/deltawalker-2.0.1

DeltaWalker 2.0.1
Merge pull request #3489 from CatTail/axureprpro

Add Axureprpro v7.0
Merge pull request #3488 from poltak/scroll-reverser

Added new cask for Scroll Reverser v1.6
Merge pull request #3467 from sigito/programmer-dvorak

Cask for Programmer Dvorak Keyboard layout.
Merge pull request #3460 from rolandwalker/add_gambit_c

add Cask gambit-c.rb