Fixes #423

Improvements to formatnum:

1. Do not format bad input, only allow digits, period and commas
2. Commas are only allowed with the R "reverse" flag that converts from "formatted" to "raw". Basically it removes commas at its simplest.
3. Turns out the commas can go anywhere. I wrote a ton of logic that checked that the commas were "correct" in the input, but turns out it doesn't matter at all...

I'll look into localization later in this draft.