Allow config file for lint options

Allow config file for lint options, with grunt task options having precedence over config file options.
```javascript
coffeelint: { 
   options: { 
      // project level config of lint options for coffeescript.
      configFile: 'coffeelint.json',
      // global options override config file options
      no_implicit_braces:     { level: "ignore" },
      indentation: { level: "error", value: 2 }
   }, 
   src: { 
     // target options override global options
      options: {  
         indentation: { level: "error", value: 4 }
      }, 
      files: { 
          src: [...]
      }
   },
   test: {
      // no target options, accept the global options
      files: { 
          src: [...]
      }
   }
},
```