added window handling protocol command to enable switch window and close window actions.
Merge branch 'master' of github.com:beatfactor/nightwatch

* 'master' of github.com:beatfactor/nightwatch:
  add doubleClick command
added closeWindow and switchWindow commands and an example test for performing facebook login authentication on digg.com website
improved selenium error handling
added alert handling protocol actions (#26)
**Added** `windowSize` protocol action and `resizeWindow` selenium command
version number bump