fig - faster, more intuitive alternative to figure function

Manage figure windows by name and prevent figure window clutter.

Use `fig` as you would the `figure` function, but with a meaningful name as the argument instead of an integer. This will help organize figure windows, prevent unnecessary clutter caused by creating new figure windows with every run of code, and will usually be noticeably faster than than traditional figure window management schemes.

See `help fig` for an example and further explanation of features and behavior.