`compile($scssCode)` will attempt to compile a string of SCSS code. If it succeeds then the CSS will be returned as a string. If there is any error, an exception is thrown with an appropriate error message.
`setFormatter($formatterName)` sets the current formatter to `$formatterName`, the name of a class as a string that implements the formatting interface. See the source for `scss_formatter` for an example.
`new scss_server($sourceDir, $cacheDir, $scss)` creates a new server that serves files from `$sourceDir`. The cache dir is where the cached compiled files are placed. When `null`, `$sourceDir . "/scss_cache"` is used. `$scss` is the instance of `scss` that is used to compile.