Fix smoothing code

Fixed dead link in Readme

merged TODO.md and TODO2.md. Also changed formatting, and added an index

Add ar-gif to README.md

https://github.com/jeromeetienne/AR.js/pull/488 Changed heading format and added proper link to TODO2.md

Added an index

Co-Authored-By: Nnavanchauhan <navanchauhan@gmail.com>

Move smoothing options to parameters and adjust defaults

Update something

Implement marker tracking smoothing from @ideolio PR #263

Remove unreferenced versions of three.js

create lean builds that only support artoolkit tracking

Marker generator: Keep the file name

Feature/markergenerator size option

Documentation Enanchement