Improved readme and changes to compile in the latest mruby version

Hi. Congratulations for this beautiful and awesome project.

I wanna help you. I've compiled this against the latest mruby version and I encountered some errors in your approach to include the headers files. It looks like the "debug.h" from mruby includes is messing your approach and causing errors on compilation.

I fixed it and changed a little bit the readme to simplify the tests using a real device or even an emulation.

Thanks in advance.