Version 0.5.0

- Redesigned the input system, so that fields are entered one at a time,
rather than all at once. This means we can do validation in a simpler
manner, and places less stress on the user to get it all right the first
time.
- Fixed a problem where cards without special text were considered
invalid.
- Enabled a nested card entry process, so that cards of the same type
can be entered sequentially.