Added example for external helper file using addCommand
Update webdriverjs.addCommand.example.js
Updated var descriptions
Updated regarding to the comments
Updated regarding to the comments
updated callback var
Update and rename webdriverjs.addCommand.example.js to webdriverio.addCommand.example.js
Rename webdriverjs.externalAddCommandHelper.js to webdriverio.externalAddCommandHelper.js
Merge pull request #320 from hanneshal/master

Added example for external helper file using addCommand