Need a field-binning function to complement the current digit-binning functions.

[sjmack]

Since the fields in version 3.. allele names are no longer defined by the number of digits (2), we can't use the digit-binning function on version 3.. allele names.

We need a field-binning function that can detect colons for defining allele-name fields, irrespective of the number of characters in the field.

[sjmack]

Ideally, a field-bining function would allow the field delimiter character to be defined in the config file.