Rename ROSLZ4_ERR -> ROSLZ4_ERROR
Touch up error code handling in roslz4
Implement streaming read functions for lz4_stream

Change name of internal buffer to buff_ from output_ as it's now used
for output and input depending on how the class is used.
Bugfix for LZ4Stream::writeStream()

roslz4_compress() will return ROSLZ4_OUTPUT_SMALL if the entire input
stream can't written to output.  The error code is only a real problem
if the output buffer was empty when compress was called.