Changed
- More consistent behavior in multiple choice listings.
- When a multiple choice question's choices are determined by code,
the image can be an uploaded file.
Added
- The `if` modifier.
- The `scan for variables` modifier.
- The `dispatch` function.
- The `has_been_gathered()` method on groups.
- More expansive error messages in debug mode.
Fixed
- Errors if variable names in `question` blocks are invalid.
- Error in `date_difference()`.
- Layout problem when sections and progress meter both turned on.