Added additional Support for customizing GPUImageFilters

* Added support for loading vec2 Uniforms into custom shader code
* Added the ability to get the GLProgram pointer from and
GPUImageFilter so that openGL routines can be used to load any type of
uniform, mainly for arrays.
* Added a frameAboutToWrite delegate to the GPUImageWriter code. This
delegate (if set) will be called every time a fram is about to be
written to the movie file. I used it to write data additional data and
system states to a text file whenever a fram is written.
Ignore any changes made to examples
gitignore update
Gitignore not playing nicely