Add comments and clean up
Remove 'node_len' param from ArrayTree constructor

Since the array tree nodes are full arrays in their own right, a global
node length does not make sense. Also, curretly it was not being
enforced.
Change use of 'ODSA' global var to 'twothreetree'

This file was overwritting the global variable ODSA. It has now being
changed to 'twothreetree' to avoid conflicts.
Add new line at end of file
Add styling for array tree and edge higlighting
Add two three tree RST file to IS book
Add new two three tree slideshow visualizations
Merge branch 'master' of https://github.com/OpenDSA/OpenDSA
Add two three tree RST file to IS book

Create copy of two three tree RST to rewrite old two three tree slide
shows.