Date Calculator PW

Do date and time calculations, in a simple date calculator app! Works just like a calculator! Two main operations:
1. Subtract two dates (time difference)
2. Add days (or other time unit) to a date
3. Subtract days (or other time unit) from a date
Common uses:
"How many days until my next birthday?"
....[your next birthday] - [today] = ________
"How many days old am I?" (or hours, minutes, etc.)
....[today] - [your birthday] = ________
"What date does that 90-day warranty expire?"
....[today] + 90 days = ________
"When is 1 million seconds from now?"
....[today] + 1000000 seconds = ________

Power-user shortcuts:
** On startup, pressing "+" or "-" auto-enters "Today" as the first expression
** "1/1/2016" + "XX days" can be reversed as "XX days" + "1/1/2016"
** Like a regular calculator, operations can be chained together (e.g. "1/1/2016" - 50 days + 2 months - [Today]).