modify bs buffer size to double the AU size
Remove unnecessary writing of nal length in the decoder

The written nal length doesn't seem to be used at all.
Merge pull request #847 from mstorsjo/remove-write-nal-length

Remove unnecessary writing of nal length in the decoder
Merge pull request #845 from huili2/bs_buffer_modif

modify bs buffer size to double the AU size at decoder