support compress & decompress by stream（block by block）

[sisong]

for decompressor

Added several lower-level APIs with little as possible source code changes, to support decompress block by block;
And updated the gzip cmdline with new APIs, the memory usage when decompress will be greatly reduced, usually <1MB!
Also, because it needs to support any .gz format (not just libdeflate), the decompress buffer will automatically adjust the size to fit the input maximum block size.

Because decompressor reused a small memory, the CPU cache hit ratio will be greatly improved, resulting in an increase in decompress speed;
In my multiple test cases, it was able to get 20%--50% faster.

for compressor

Added several lower-level APIs with minor source code changes, to support compress block by block;
And updated the gzip cmdline by new APIs, the memory usage when compress will be greatly reduced;
The memory requires is related to the block size set and compress level, not related to input file size; when the block size is 2 MB and compress level is 12, the memory usage ~ 13 MB.
These new APIs can be used for multi-threaded parallel compression, and there is almost no loss of compress ratio.

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( I used libdeflate for my multiple actual projects and make a lot of feature changes; Hopefully commit some useful changes back to libdeflate. )