Optional block compression using LZ4

[incubos]

On write:

• Fill a block until 64KB reached
• Add a block header with payloads offsets
• Compress the block using LZ4
• Add a segment header with blocks offsets

On read (getDocumentById()):

• Find the block using blocks offsets
• Decompress the block into temporary buffer (possibly stopping after having decompressed enough bytes)
• Slice the payload using payloads offsets

[incubos]

As an alternative we could use https://github.com/luben/zstd-jni thanks to support for dictionary compression (having trained dictionary using all the payloads).