Compressor support

Adds support for new filters and compressors to add support for UglifyJS.

Filters

barbeque.compressor.UglifyJSFilter

A filter that uses UglifyJS to compress JavaScript code.

Integration:

COMPRESSOR_JS_FILTERS = [
    'barbeque.compressor.UglifyJSFilter',
]

Compressors

barbeque.compressor.UglifyJSSourcemapCompressor

A compressor that compiles javascript code using UglifyJS and generates a proper sourcemap.

Integration:

COMPRESS_JS_COMPRESSOR = 'barbeque.compressor.UglifyJSSourcemapCompressor'