[RFE] given a manifest, return keywords used

[Vincent Batts]

Something like:

$ gomtree -f ./foo.mtree -list-used

to return a parseable string of keywords used, such that subsequent tooling could easily choose to validate the manifest against that set of keywords or less (i.e. ignoring mtimes).

[imsteev]

working on this on 739746. I'm wondering if instead of just returning a slice of keywords, we could create something like a Collector struct that would output meaningful information about the mtree spec. For example:

type Collector struct {
   CollectType1
   CollectType2
   .
   .
   .
}
ParseSpec(r io.Reader, collectorArgs... ) (*DirectoryHierarchy, *Collector, error) {
}

This has no effect on gomtree's functionality, but it might be a nice feature to have, especially when working with mtree files that represent a really large directory.