This extends the existing Rust code to handle conditional
replacement. The replacement of field names and filters to text
remains in Python, so that add-ons can still define their own
field modifiers.
The code is currently running the old Pystache rendering and the
new implementation in parallel, and will print a message to the
console if they don't match. If you notice any problems, please
let me know.
the current code was causing the day to move backwards:
at day 7 hour 23:59, elap is 1
at day 8 hour 0:59, elap is 0
at day 8 hour 1:59, elap is 0
at day 8 hour 2:59, elap is 1
at day 8 hour 3:59, elap is 1
at day 8 hour 4:59, elap is 2
as mentioned in https://github.com/ankitects/anki/pull/416
