Regexes can follow `!`

Fixes matthiasmullie#197

Require that a regex has some content

Otherwise, the `//` that start a comment could be misread
as regexes.

Fixes matthiasmullie#196

Improve regex detection

Fixes matthiasmullie#195

Allow `=` inside regexes

A fix for something else introduced a potential issue that when
regular expressions have a `=` inside them, they wouldn't be
recognized as such.

This should make the regex detection more robust by checking
the surrounding code, instead of limiting what can be inside.

Quote url() uri's with quotes in them

Fixes matthiasmullie#193

Fix newline trimming around tilde

Fixed matthiasmullie#185

Don't collapse newlines after 'continue'

Fixes matthiasmullie#178

Add test for matthiasmullie#163

Fix unitless flex-basis, for IE

Fixes matthiasmullie#159

php-cs-fixer