Uniform Buffers API implementation

Implemented the necessary functions
for the API level implementation of
glBindBufferBase and glBindBufferRange.
Also cleaned up the TransformFeedback
API functions a little for uniformity
with uniform buffers.

Change-Id: Iccc835f175d4e8bc4ee030343936714b7ff224ac
Reviewed-on: https://swiftshader-review.googlesource.com/3030
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>

src/OpenGL/libGLESv2/Buffer.cpp

diff --git a/src/OpenGL/libGLESv2/Buffer.cpp b/src/OpenGL/libGLESv2/Buffer.cpp
index 42a1eea..0c164fa 100644
--- a/src/OpenGL/libGLESv2/Buffer.cpp
+++ b/src/OpenGL/libGLESv2/Buffer.cpp
@@ -64,7 +64,8 @@
 
 		if(data)
 		{
-			memcpy((void*)mContents->data(), data, size);
+			char *buffer = (char*)mContents->data();
+			memcpy(buffer + mOffset, data, size);
 		}
 	}
 }