Add support for MaxiCode on iOS

[zhaoshengjun]

Hi Eddy,

Just tried this plugin, works great! I am facing a small issue here with MaxiCode on iOS.

As you specified in the readme file, MaxiCode is only supported in Android. But I wonder if you can add it to iOS as well? I've found some code on github:

https://github.com/TheThingSystem/steward-ios-library/tree/master/Bootstrap/ZXingObjC/maxicode

Please check it. Thanks!

[EddyVerbruggen]

On iOS we can only scan types which are built in to the iOS scanner. Full list here, Apple doesn't support Maxicode and I'm not switching to ZXing.