[#48] Fix freeze/thaw identity on empty lazy seqs
v2.6.3
Bump deps
Add experimental LZ4 compressors
LZ4: use fast decompressor
EXPERIMENTAL: Make LZ4 the default Nippy compressor (back-compatible for header'ed data)
Encode compression type in Nippy header, major refactor/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.
  * Simplification of `thaw` API: Nippy v1 support is now automatic
    & configuration-free (performance impact in most cases is negligible).
Update benchmarks
Lock-free memoized type test
Bump deps
v2.7.0-SNAPSHOT
EXPERIMENTAL: Support keyword-id extensions (#50)