Support key-value tags, at least in ls filters

[Riebart]

In some cases, it is useful to identify classes of tags, and potential values (e.g. AWS key-value tag semantics).

Support could be limited to enabling regular expression matching of tags, where a ledger entry's tags must either be a non-empty intersection with the list of tags, or match at least one of the patterns in a tag_patterns list. This would allow you to filter on anything where

Client=(ACME|BigCorp|.*Design)

as opposed to currently needing the more verbose current requirement where the tag list of an entry intersects with

["Client=ACME","Client=BigCorp","Client=ArchitectureDesign"]