Decompression works

Compression to file

Fix weird line of code

Rename huffman_element.rs to huffman_node.rs

Refactored weighted node into tuple to reuse existing enums

Refactor huffman_elements to drop weight property as tree is built

Tweak binary description

Basic structopt config for rhuff-compress

Implemented HuffmanDecoder from HuffmanTree

tweak cargo description

Switched project organisation to workspaces to support a binary with additionnal dependancies

Renamed add_occurences to add_occurences_to_symbol plus documentation

Add MIT license

Switch binary tree to binary heap

Removed unnecessary abstraction