Right now does not add padding at the end of the buffer.
This seems not necessary but may cause problem on some platform. If needed
we will add this padding (only 2 more vertices).
This does not include all the struct and type renaming. Only files were
renamed.
gwn_batch.c/h was fusioned with GPU_batch.c/h
gwn_immediate.c/h was fusioned with GPU_immediate.c/h
gwn_imm_util.c/h was fusioned with GPU_immediate_util.c/h