Parsing static resources spec.

• Line starting with word set is start of ResourceSet definition.
• Line starting css, js or jsx defines Resource.
• Line starting with ignore defines that some file should be ignored by checker.
• ALL other lines are ignored

Sample spec

 ignore main.css

 set a
   js  a.js 
   css a.css
   css common.css

 set b
   js  b.js    
   css b.css
   css common.css