Added preprocessorOpts option

Renamed preprocessorOpts to preprocessOpts

Added preprocessOpts to README

Added an import test for preprocessOpts functionality testing
Merge branch 'preprocessor-options' of https://github.com/prewk/grunt-suitcss into preprocessor-options

* 'preprocessor-options' of https://github.com/prewk/grunt-suitcss:
  Added an import test for preprocessOpts functionality testing
  Added preprocessOpts to README
  Renamed preprocessorOpts to preprocessOpts
  Added preprocessorOpts option