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-d3d11/d3d11-subsystem.cpp

@@ -421,6 +421,11 @@ gs_device::gs_device(gs_init_data *data)
 	device_setrendertarget(this, NULL, NULL);
 }
 
+const char *device_preprocessor_name(void)
+{
+	return "_D3D11";
+}
+
 gs_device *device_create(gs_init_data *data)
 {
 	gs_device *device = NULL;