Add option for raw compass config data

[jacksleight]

The grunt-contrib-compass module has a raw option which allows you to parse in additional configuration options (written in ruby) that are otherwise unavailable. This would be very useful in gulp-compass.

Compass doesn't expose all of its options through the CLI, which this task makes use of. If you need an option not mentioned below you can either specify a path to a config.rb file in the config option or embed it directly into the raw option. Options defined in your Gruntfile will override those specified in your config.rb or raw property. config and raw are mutually exclusive.

For example, with grunt I use this to specify a custom asset_cache_buster method.

[appleboy]

related #37