BUGFIX: don't try autocleanup inside system dirs

This safety feature addresses #2650 somewhat indirectly.
A list of system directories is defined.  When the uninstall
process encounters a "system directory" it does not touch that
directory at all
- no chmod on that dir
- no search for broken symlinks in that dir
- no cleanup of .DS_Store files in that dir
Explictly listed files from a pkg receipts are not affected by
this change.  Individual files will still be removed, even if
those files are in a special "system directory"
doc: tweaks to CONTRIBUTING.md

- subheads so we can link directly to CONTRIBUTING.md#cask-stanzas
- clarification on naming `pkg` Casks
- fix repetitive language
doc: drop version numbers from end of Cask names
Vienna RSS 3.0.0_beta20
Yemuzip: new formula.

Yemuzip is a zipper that allows to exclude the osx-specific
metadata (__MACOSX, ._*, etc.)
Merge pull request #3290 from dpo/master

Yemuzip: new formula.
Merge pull request #3291 from cubranic/vienna-30-beta20

Vienna RSS 3.0.0_beta20
Upgrade Thunder.app to v2.4.0.1356_Beta
Add docs for Caskfiles
Add dotfiles section to Caskfile docs
Merge pull request #3292 from tolbkni/thunder

Upgrade Thunder.app to v2.4.0.1356_Beta
New cask: vassal 3.2.11
Update owncloud.rb

updated to version 1.5.2.2335
Merge pull request #3295 from phpwutz/patch-1

Update owncloud to 1.5.2.2335
Merge pull request #3293 from ndr-qef/doc-automation

Add docs for Caskfiles and automation
Merge pull request #3294 from res0nat0r/vassal-3.2.11

New cask: vassal 3.2.11
Merge pull request #3286 from rolandwalker/doc_contributing_tweaks

doc: tweaks to CONTRIBUTING.md
Merge pull request #3285 from rolandwalker/doc_cask_name_drop_version

doc: drop version numbers from end of Cask names
rename flash-decompiler.rb

to flash-decompiler-trillix.rb
per naming rules in CONTRIBUTING.md
rename fm-designer.rb

to b2designer.rb
per naming rules in CONTRIBUTING.md