NFD

https://gerrit.named-data.net/3359 implements face show command.
patchset1 focuses on output format, and only handles successful case; I'll handle failure case in a later patchset.

Example output:

vagrant@m0212:~/NFD$ nfdc face show 258
  faceid=258
  remote=fd://25
   local=unix:///run/nfd.sock
counters={in={5510i 14d 0n 291775B} out={14i 968d 0n 636549B}}
   flags={local on-demand point-to-point local-fields}
vagrant@m0212:~/NFD$ nfdc face list | grep faceid=258
  faceid=258 remote=fd://25 local=unix:///run/nfd.sock counters={in={5521i 14d 0n 292337B} out={14i 972d 0n 638396B}} flags={local on-demand point-to-point local-fields}

While the design suggests a key-value pair format for each attribute with a space in between, I decide to keep the existing {} style since it shouldn't cause much difficulty for script consumption as long as parentheses are paired correctly.
Attributes are aligned at =, which is consistent with existing status show command.
I moved local on-demand point-to-point into flags to satisfy key-value pair format. While they are technically not flags in FaceMgmt protocol, from user point of view they are no different from flags, thus it makes sense to list them together with local-fields. This change applies to nfdc face list command as well, since they are generated from the same code.

https://gerrit.named-data.net/3359 adds unit tests. It required quite a bit of refactoring.

https://gerrit.named-data.net/3633 adds face create command.
An FindOrCreateFace component is introduced, given that other commands in RIB etc will need to find or create faces as well; this is intended to be the replacement of FaceIdFetcher.

https://gerrit.named-data.net/3661 adds face destroy command.

FindFace::execute(const FaceQueryFilter&, ..) overload is not strictly necessary for this command, but it's needed for face list [[remote] <uri>] [local <uri>] [scheme <scheme>].
A consequence is that FaceUri is first converted to string, and then parsed back from string.

I wonder why FaceQueryFilter stores strings instead of FaceUris?

https://gerrit.named-data.net/3681 rewrites face list to support filtering. The implementation is based on FindFace and is separate from FaceModule::fetchStatus. FaceModule::fetchStatus is still needed for use by status report.
However, patchset1 is not working with real NFD: FindFace::canonize is stuck within face.processEvents(), possibly related to #1785. I'm still investigating.

face destroy is also not working when invoked with FaceUri due to the same FindFace::canonize problem. I will hold off adding more commands relying on FindFace::canonize until this is fixed.
Note that face show is unaffected despite it uses FindFace, because it only accepts FaceId.

The current FindFace::query implementation always fetches faces/query dataset even if the filter is empty. It would be more efficient to fetch faces/list dataset. This optimization will be added in a later patchset or another commit. https://gerrit.named-data.net/3683 adds FaceQueryFilter::empty() function to support this optimization.

face create is not working with real NFD: I thought faces/create command response contains RemoteUri (and assumed so in unit testing) but it doesn't. https://gerrit.named-data.net/3682 fixes this bug.

https://gerrit.named-data.net/3704 deprecates nfdc create and nfdc destroy. These commands print a deprecate notice to stderr when used.
nfdc(1) manpage is kept unchanged. It will be rewritten after all legacy nfdc commands are deprecated.