Changelog:
==========
Add SeekableZstdFile class, it's a subclass of ZstdFile, supports Zstandard Seekable Format.
Add mode argument to ZstdFile.flush() method, now it can flush a zstd frame.
Add read_size and write_size arguments to ZstdFile.__init__() method, can work with Network File Systems better.
Optimize ZstdFile performance to C language level.
Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>
