Support PPMd; Fix Zstd and Append Mode

Changed

• PPMd: Use stream encoder/decoder instead of buffered one.
• PPMd: Use [email protected] 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.