remove base64 dependency

README

main: fix length issue for large files

add compression ratio and use full hamlet as test

main: implement simple cli interface

allow encoding and decoding as bytes

express frequency using u32

main: implement huffman encode and decode

bitvec: use bit_vec crate

traverse_huffman_tree should return the huffman codebook

decouple construction of frequency table

tree: sort nodes by value if freq is equal

initial commit