Bump deps
Add experimental LZ4 compressors
LZ4: use fast decompressor
EXPERIMENTAL: Make LZ4 the default Nippy compressor (back-compatible for header'ed data)
Update benchmarks
Encode compression type in Nippy header, major housekeeping

Housekeeping includes:
  * Importing useful encryption+compression stuff into primary ns
    for lib consumers.
  * Promoting a number of things from Alpha status.
  * Exceptions are now all `ex-info`s.
v2.7.0-SNAPSHOT