Add Buffer Management to SnappyInput Stream

[chietti]

SnappyOutputStream uses a buffer management system to reduce memory pressure and GC overhead. The same mechanism would be helpful in SnappyInputStream as well.

We want to use Snappy for protocol compression in a high volume system. Currently we can see a significant increase in GC overhead due to the massive amount of buffers being allocated in SnappyInputStream. Adding the same BufferAllocator as in SnappyOutputStream would help to significantly reduce the amount of allocated memory.

Btw: we use both variants, the chunked one generated by SnappyOutputStream and the raw one used by a native Snappy implementation.

[SHaaD94]

Hi, @xerial.
I would be happy to raise a PR for this.
Would you approve such change?