Fixing several items for 1.1.0 release

  * Added NDFD::DWML class to handle parsing of XML responses
  * Added Travis CI testing on 2.1.1
  * Explicitly changed to simplecov 0.7.1 because of outstanding bug (see https://github.com/colszowka/simplecov/issues/281)
  * Refreshed VCR cassettes
  * Removed GML api methods (the endpoints on the service don't work as expected)
  * Removed XSLT translation (it did not handle responses with multiple lat/longs) in favor of pure ruby parsing
  * Removed vendor folder (previous reference to noaa-dwml-to-json-xslt)
  * Updated documentation regarding GML methods