All-intended-features release as 'postcss-extend'

Only known ongoing issues of note are some odd results (not even crashes, just results) when it attempts to correctly process CSS that has infinite @extend loops when @media statements are involved.

So, don't expect infinite loops to go over smoothly?
Yes, you shouldn't be using them anyway.

Features added since postcss-simple-extend (aka: v0.3.x and earlier) :

• Works with silent '%' selectors
• Works with existing (real) rules at root
• Strict behavior of standard placeholder, and relaxed behavior of % (silent) classes
• Elimination of duplicate selectors on extended rules
• Removal of otherwise empty code blocks (from only-extension)
• Acts recursively (both directions thanks to 'living log' behavior, and selective-recursion)
• Targets sub classes and extends them with pseudo version of the extended
• Acts recursively on sub classes
• Finds it's exisiting sub classes (shared scope in media) and pulls declarations into them when possible
• If inside @media does a declaration pull for anything outside @media
• Correctly handles re-declarations, by ignoreing incoming via @extend (original overwrites)
• Order of naming remains a predicatable add-to-tail fashion, and follows vertical order, then recursion in priority
• Detects, and gives a trace of all rules that are part of an infinite loop of @extend recursion.