Promote several properties to public API.

The properties

  * layers
  * queryVisible
  * url
  * layerUrls
  * infoFormat
  * vendorParams
  * format
  * formatOptions

should all be visible in the public API since they are essentially very
convenient to use when customizing the control.
Reformat documentation to match surrounding doc.
Remove end-of-line whitespace.

The license header is left untouched, to keep it the same in all files.
A seperate commit will probably deal with this
Merge pull request #872 from marcjansen/wmsgfi-api

WMSGetFeatureInfo API enhancements