Rewrite SDK in Android Studio

[netguycode]

This is going to be quite useful as its easy for devs to directly experiment with controlling the led and printer via shell commands.

This will at least allow them to test if their hardware is working at a basic level before starting to code.

Also updated the readme to give a more specific pointer of what files to start to read to learn more on using it.

I've attempted to convert it to android studio, but hit a problem. I think the SDK is actually for eclipse IDE.

I think it's best to just use the SDK code as a reference instead and just manually rewrite it in android studio if needed.

Originally posted by @mofosyne in #13 (comment)

[netguycode]

@mofosyne I've started this and re-written the classes in Kotlin.

Developing a new app to implement the SDK in this week.