RFE: some nice to have features

[magsoftware]

1. Possibility to define a rule to omit a data row (under certain conditions)
2. Possibility to define actions when there are 2+ identical data rows
3. Possibility to define default values for a field (with markers for empty field see example below)
4. Possibility to define any code for a field, eg.

if field_value == '-':
    field_value = 0

5. possibility to define a python function (callback) called for every row
6. the same for the whole file