URLRewrite to set paths as absolute URL

Related to Issue #98
Pass in url() for absolute site url rewrites

Decoupled url() from #104
Pass in url() to rewrite for absolute url
https://github.com/CodeSleeve/asset-pipeline/issues/103
Merge remote-tracking branch 'origin/pr/104' into testing
Merge remote-tracking branch 'origin/pr/108' into testing

Conflicts:
	src/Codesleeve/AssetPipeline/Filters/URLRewrite.php
takign out null from to() in config
https://github.com/CodeSleeve/asset-pipeline/issues/106
https://github.com/CodeSleeve/asset-pipeline/issues/110
fixing bug
fixing image composer bug
fixing bug in imageTag