bump lz4-sys version

Bump 1.18.131

Add Encoder.writer() and Decoder.reader() methods (thanks to @PaulGra…

…ndperrin)

Bump 1.14.131

Bump 1.13.131

Bump 1.12.131

Merge pull request #6 from cmr/nicer-docs

Don't export the modules in the public API.

Bump 1.9.131

Bump 1.8.131

Update lz4 to r129