add isCameraModeChanging

used to determine if the camera mode is currently changing
Merge pull request #112 from jrmsklar/is-camera-mode-changing

Added isCameraModeChanging
Update README.md
Podspec, bump version to 0.2.0
Update README
PBJMediaWriter, fix debug logging
PBJVision, add support for focus locking, focus adjustment, exposure locking, exposure adjustment
PBJGLProgram, abstracted out GL shaders
PBJGLProgram, minor api change
create strings for shader attributes
PBJGLProgram, added comments
PBJMediaWriter, don't invalidate timestamps when finished
PBJVision, add cancel functionality, media writer re-use
PBJViewController, add cancel checking
PBJVision, add support for variable frame rates, 120 fps, slow mo
update readme
Podspec, update summary
PBJVision, add comments
PBJVision, add clang pragma for deprecated methods
Sample project, minor cleanup
PBJVision, remove dead code
PBJVision, minor code cleanup