Add developer scripts

Automates the procedure documented in CONTRIBUTING.md
Overhaul USAGE.md

- Include all current commands
- Use new functionality to skip explicit "brew tap" commands
- Document all forms for specifying Casks (URI, etc)
- Demote "Additional Taps" section to near the end
- Other small tweaks too numerous to list
Spin out HACKING.md from CONTRIBUTING.md

Create a bunch of guidelines/FAQs based on stuff gleaned from
PR discussions and IRC.  Obviously this is just a starting
point.
Add project_stats script

Queries git database to get statistics on project or release.
Usage in project_stats -help
add missing user feedback during pkg uninstall

Consistent between uninstall keys.  Also give initial feedback
first, before any other action.
eclipse-ide: update to 4.3.1
eclipse-platform: update to 4.3.1
tikz-editor.rb Cask missing .app extension

fails install without this change
Allow cask instance methods within blocks

This covers after_install and after_uninstall.  The caveats
stanza is treated separately.
Add perian
Use latest soundcleod

Use latest version of SoundCleod.app. #2448 #2452
Merge pull request #2458 from jonotrujillo/latest-soundcleod

Use latest soundcleod
Add artifact caskroom_only

The difference between specifying caskroom_only and specifying
no install artifact at all is: caskroom_only respects the
uninstall stanza.  Obviously this is not the best implementation:
uninstall support should be refactored into the base class.
Merge pull request #2459 from rolandwalker/cask_only_artifact

Add artifact caskroom_only
Merge pull request #2457 from jimbojsb/perian

Add perian
add perian caveats indicating project status
Merge pull request #2456 from rolandwalker/instance_methods_in_blocks

Allow cask instance methods within blocks
Merge pull request #2445 from rolandwalker/uninstall_messages

add missing user feedback during pkg uninstall
Merge pull request #2433 from rolandwalker/usage_doc_cleanup

Overhaul USAGE.md
Merge pull request #2390 from rolandwalker/hacking_doc

Spin out HACKING.md from CONTRIBUTING.md