various updates

Hardeep can you confirm that the new config_file_element.md renders ok and that the links to it also work as expected -- wasn't able to test. Also please close these issues once deployed: 
https://github.com/phonegap/build/issues/237
https://github.com/phonegap/build/issues/235
https://github.com/phonegap/build/issues/234

Cheers dude!