Support simple arithmetic expressions in data entry
I often switch between Beeminder and a calculator while entering data: ie. I want to enter 6 sessions of 24 minutes, or however many more locations I've read on a book (ie. I'm now on 2346 and on previous datapoint I was at 2077) odometer goal doesn't cut it, I read several books simultaneously); this is particularly cumbersome on mobile. Let me enter instead "6 * 0:24" and "2346 - 2077".