Update .gitignore to allow for _todo.js notes file in each sketch
Update .gitignore to allow for _todo.js notes file in each sketch

* Recently found myself creating a scratch space of functions / algorithms that are not quite ready for inclusion.
    - This allows them to exist side-by-side with theiry actual sketch without risking accidentally comitting them and creating noise in the git history.

brianhonohan/sketchbook,brianhonohan/sketchbook,brianhonohan/sketchbook