Merge pull request #388 from gobackspaces/master

Synthesize contextQueue to allow for compilation of project
Fixed a couple of the warnings about not having a root view controller in the sample applications. Made setting the video camera rotation a little more thread safe.
Added a Lanczos resampling filter, and a new section in the SimpleImageFilter example that shows how resampling works.
Per Joel Teply's suggestion, fixed the RGB dilation and erosion filters to properly take into account alpha channel values.
Added a cache for shader programs to speed up filter reuse. Fixed a threading issue with the tone curve filter. Fixed an overrelease of an audio processing queue.
The frame processing completion block should now be handled correctly for filter groups.
Validate the crop rect before assigning it.
Fixed typo in README.md

In the example code for adding a custom filter to a video feed, replaced "thresholdFilter" with "customFilter".
Started adding an average color processing filter. Fixed an issue with two-pass filters introduced with the recent shader caching commit. Added a default initializer for generic filters.
Merge pull request #415 from oxling/master

Fixed typo in README.md
Merge pull request #410 from jad/master

Crop filter: validate the crop rect before assigning it
Completed the average color filter and created a solid color fill generator.
Updated the ColorObjectTracking example to use GPU-based averaging, which makes it operate at 30 FPS. Improved the precision of the averaging filter in certain cases.
Added a luminosity extractor to go along with the new average color one.
the GPUImageToneCurveFilter now can take into account the rgbcomposite channel together with the separate r, g, and b channels
Added a threshold filter that takes the average luminance of a scene into account. Updated the documentation for the new filters.
Merge pull request #428 from ahfarmer/tone-curve-composite

the GPUImageToneCurveFilter now can take into account the rgbcomposite c...
Update inputCamera property after rotating camera.
Added two new properties on the camera inputs: horizontallyMirrorFrontFacingCamera and horizontallyMirrorRearFacingCamera which determine whether the camera should be mirrored in those positions. Fixed a potential issue with movie playback in the Simulator.
Merge pull request #430 from ltbl/master

Update GPUImageVideoCamera inputCamera property after rotating camera