Merge pull request #203 from martin-g/uri-utils

Minor improvements in URIUtils
Close #210
Added test for empty strings (loosely related to #207)
String comparison now ignores quote type e.g. "value" is the same as
'value'. Close #207
Adding support for unknown at rules. Fixed serious bug in nested rulesets
handling too. #206
Added support for expression in those directives. Close #206
Merge branch 'master' into 199-inline-source-maps