Clean up for releasing

[neizod]

main

• drop support for python2 and pypy? (so we can use the robust syntax like generators...)
• rewrite InfiniteList by using metaclass...
• drop monkey patching (Fraction.decimal)
• drop duality -- it's a wired concept and hard to use!
• make sure it pass PEP8.

chores

• better docs.
• update github wiki.
• fix trailing white spaces.