Behavior of `MARC::Record` `data_fields`, `each_data_field`, and `data_fields_by_tag` extension methods is counterintuitive

[dmolesUC]

data_fields_by_tag

Expected

• returns all data fields in the original record, including fields with non-standard tags (e.g. "FFT" for TIND records)
• returns only MARC::DataField objects

Actual

• returns only fields with valid numeric tags in the range 010-999
• returns MARC::ControlField objects, if they have a tag in the data field range

data_fields / each_data_field

• returns/yields all data fields in the original record, including fields with non-standard tags (e.g. "FFT" for TIND records)
• returns/yields only MARC::DataField objects
• preserves the original order of fields

Actual

• returns/yields only fields with valid numeric tags in the range 010-999
• returns/yields MARC::ControlField objects, if they have a tag in the data field range
• reorders fields by tag

[dmolesUC]

See BerkeleyLibrary/tind #4 for an example of the kind of problem this can cause.

[dmolesUC]

Note, though, that fixing this could be a breaking change for users that rely on the order.