Normalizing missing record fields

[jackfirth]

Sometimes records have missing fields that actually represent default values, or are otherwise significant. There should be some support in rebellion/collection/record for these use cases:

• I have a record and I know what fields it can have. Missing field X should be the same as setting it to 0, missing field Y should be the same as the empty string, etc.
• I have a record and I know what fields it can have. All missing fields should be turned into present fields, and there's no field-specific logic involved.
• I have many records and I don't know what fields they can have. Some records have fields that other records don't. I need to find out which fields are present in at least one of the records, then transform the records such that those fields are set in every record.

@samdphillips Does that about cover the use cases you ran into?

[samdphillips]

Here is another use case, that could be generalized from the first two:

• I have a record and I know what fields it can have. Missing field X should be computed from the record.