ability to extract column substrings

[zacchiro]

[ context: this thread on the Ledger-cli maling list https://groups.google.com/forum/#!topic/ledger-cli/AfGKE2Svv0s ]

Currently, the granularity of icsv2ledger addons is that of columns: extra columns present in the input CSV can be referenced from templates.
It would be nice if addons granularity could be more fine grained than that, for instance by supporting (named) grouping in regexps and adding the ability to reference them from templates. This would allow very flexible information extraction for banks that put a lot of information in transaction descriptions.

With many thanks for maintaining icsv2ledger!