Frame processors

[natario1]

Add APIs and functionality for Frame processors.

• Added FrameProcessor interface
• Added Frame class
• Added addFrameProcessor, removeFrameProcessor APIs
• Added tests

Fixes #48
Fixes #74

[codecov]

Codecov Report

Merging #82 into master will increase coverage by 0.8%.
The diff coverage is 75.4%.

Impacted Files	Coverage Δ	Complexity Δ
...com/otaliastudios/cameraview/CameraController.java	27.1% <ø> (ø)	18 <0> (ø)	⬇️
...ain/java/com/otaliastudios/cameraview/Camera1.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...c/main/java/com/otaliastudios/cameraview/Size.java	94.1% <100%> (ø)	11 <1> (ø)	⬇️
.../java/com/otaliastudios/cameraview/CameraView.java	69.5% <73.9%> (+1.1%)	98 <3> (+3)	⬆️
.../main/java/com/otaliastudios/cameraview/Frame.java	96.5% <96.5%> (ø)	11 <11> (?)
...a/com/otaliastudios/cameraview/CameraListener.java	10% <0%> (+10%)	1% <0%> (+1%)	⬆️