expose ability to set compression level for LZ4-HC introduced in lz4 r113
cache constructed HC compressors
Add test case for customized-level compressor.
use AtomicReferenceArray for caching.
pre-instantiate all compressors.
Merge pull request #1 from linnaea/compcache

Create all compressors up-front.
Update javadoc
Drop LZ4HCCompressor interface
Merge remote-tracking branch 'jpountz/master'
Merge branch 'master' of github.com:linnaea/lz4-java into linnaea-master

Conflicts:
	src/java/net/jpountz/lz4/LZ4HCJNICompressor.java
Merge branch 'linnaea-master'