Share compress output buffer among TreeWriter

There's individual instance of `OutStream` within each TreeWriter created by `WriterContext#createStream` method. Within `OutStream`, there are totally 3 buffers: 

• current: the regular input buffer holding uncompressed, unencrypted bytes.
• compress: the output buffer holding compressed bytes 
• overflow: same as "compress" but only used when the last compression output is larger than remaining capacity of compress buffer. 

Potentially the compress and overflow buffer doesn't have to be allocated individually within each OutStream object, but shared across all of them so to save memory. This ticket is trying to achieve that and obtain saving number with some sort of benchmarking(yet to be defined).