Reorganization of library structure to better match Arduino spec (#20)

Note, this will also require to you "uninstall and reinstall" the Arduino library due to the library file location changes.

Reviewed-on: https://git.pinkduck.xyz/awonak/libGravity/pulls/20

library.properties

@@ -0,0 +1,10 @@
+name=libGravity
+version=2.0.0beta2
+author=Adam Wonak
+maintainer=awonak <github.com/awonak>
+sentence=Hardware abstraction library for Sitka Instruments Gravity eurorack module
+category=Other
+license=MIT
+url=https://github.com/awonak/libGravity
+architectures=avr
+depends=uClock,RotaryEncoder,U8g2