dev(hansbug): add comparison benchmark to google jax

dev(hansbug): create flatten_values and flatten_keys

doc(hansbug): use gh-pages as documentation deploy page

doc(hansbug): update documentation for mapping and filter_ && update README's demo

test(hansbug): add benchmark for the basic operations and functions

dev(hansbug): refactor all the __ixx__ operators

dev(hansbug): optimize for TreeValue's getattr