miurahr/py7zr: Support PPMd; Fix Zstd and Append Mode

Hiroshi Miura, Kyle Altendorf, Andre Brait, , , Rodrigo Prado, Vincent Poulailleau, , Ma Lin &
Changed PPMd: Use stream encoder/decoder instead of buffered one. PPMd: Use ppmd-cffi@v0.3.1 and later.(#268) Added PPMd compression/decompression support.(#255) New API to set methods to set header encode mode, encode or encrypted.(#259) Support Python 3.9.(#261) Support arm64/aarch64 architecture on Linux.(#262) Fixed Append mode cause error when target archive use LZMA2+BCJ.(#266) Fix zstandard compression/decompression.(#258) Deprecated Drop support for python 3.5 which become end-of-life in Sept. 2020.
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