Create UI to type a text (for alphabet extraction)

This version has a UI to type a text, that upon keypress is automatic
parsed and feeded into the Huffman algorithm.

The Huffman class has been refactored, and the Processing.js code
removed.

index.html still has (commented-out) code to load and run a script in
runtime.
Remove unused elements from index.html
Format code previous refactoring
Refactor Huffman Node class: power constructor

Node class refactored according to Douglas Crockford's power constructor
idiom. See "Douglas Crockford: Advanced JavaScript" video under
http://www.youtube.com/watch?v=DwYPG6vreJg.
Refactor Huffman class: power constructor
Refactor huffman's API

Methods visibility reworked to expose only the public members of the
huffman class.
Fix sorting of nodes in huffman's algorithm