Make a number of key optimizations

- Changed glMapBuffer to glMapBufferRange to allow invalidation.  Using
   just glMapBuffer alone was causing some unacceptable stalls.

 - Changed dynamic buffers from GL_DYNAMIC_WRITE to GL_STREAM_WRITE
   because I had misunderstood the OpenGL specification

 - Added _OPENGL and _D3D11 builtin preprocessor macros to effects to
   allow special processing if needed

 - Added fmod support to shaders (NOTE: D3D and GL do not function
   identically with negative numbers when using this.  Positive numbers
   however function identically)

 - Created a planar conversion shader that converts from packed YUV to
   planar 420 right on the GPU without any CPU processing.  Reduces
   required GPU download size to approximately 37.5% of its normal rate
   as well.  GPU usage down by 10 entire percentage points despite the
   extra required pass.

libobs/graphics/graphics-imports.c

@@ -40,6 +40,7 @@ bool load_graphics_imports(struct gs_exports *exports, void *module,
 {
 	bool success = true;
 
+	GRAPHICS_IMPORT(device_preprocessor_name);
 	GRAPHICS_IMPORT(device_create);
 	GRAPHICS_IMPORT(device_destroy);
 	GRAPHICS_IMPORT(device_entercontext);