IMPORTANT FIX: small strings weren't getting a proper UTF-8 encoding (xkihzew)

`(.getBytes <string>)` was being used here instead of
`(.getBytes <string> "UTF-8")` as is correct and done elsewhere.

This means that small UTF-8 strings may have been incorrectly stored
in environments where UTF-8 is not the default JVM character encoding.

Bug was introduced in Nippy v2.6.0, released 9 days ago (2014 Mar 30).

*********************************************************************
Please check for possible errors in Unicode text written using Nippy
v2.6.0 if your JVM uses an alternative character encoding by default
*********************************************************************

Really sorry about this, not sure how this slipped in.

Thanks to @xkihzew for the bug report.
v2.6.1
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
v2.7.0-SNAPSHOT