additional compression distances

[chrislit]

• [x] PAQ (via https://github.com/observerss/paq)
• [x] LZSS (https://github.com/rumbah/pylzss)
• [ ] PPMd (cf. #32)
• [ ] ZPAQ?
• [ ] LZ4 (https://github.com/python-lz4/python-lz4)
• [ ] LZO (https://github.com/jd-boyd/python-lzo)

[chrislit]

putting this of until 0.7 PPMd is going to be a pain as is ZPAQ and LZ4 & LZO aren't going to be all that interesting