Add option to match against a stream/file of input paths

[hollasch]

This is for the task of matching entries not from the file system, but instead from a list of entries streamed from stdin.

This would possibly use a switch like --filter, --stream, --stdin, or --input. Following convention, you could also use the simple single hyphen - as the standard option. This is a bit confusing, however, as pathmatch does not normally take a filename of patterns.

[hollasch]

Stubbed in with commit fd7af16.