Add GPUImageColorInvertFilter implementation

Signed-off-by: Wenwei Cai <stanley.w.cai@gmail.com>
Add x86 support for JNI library

Signed-off-by: Wenwei Cai <stanley.w.cai@gmail.com>
Add GPUImageHueFilter support

Signed-off-by: Wenwei Cai <stanley.w.cai@gmail.com>
Add a small ShaderToString Utility

- Just convert Shader to multiline Java String

Signed-off-by: Wenwei Cai <stanley.w.cai@gmail.com>