ios: add support for new SDK features [#11]

Add support for setting following 3 features:
- use device orientation
- no partial matching
- small target support
ios: add compiler-flags in plugin.xml

This way we can save user some time to add the compiler flags themselves. 
This is an intermediate state. Finally we all be supporting both ARC and
non-ARC projects as mentioned in issue [#6].
Update README

- Remove extra steps, they are taken care by the plugin.xml
- Replace `cordova` by `phonegap`
- Add reference section