Now prints JSON versions of feeds when given --json.

Also handles flags correctly by using @local_argv inside main() rather
than the unmodified @ARGV - a bug lingering from copypasta of wrt-display
code.

Uses JSON::Feed, for the moment, although it might be worth just rolling
my own to avoid the dependency.

Adds:

  - feed_print_json_recent()
  - feed_print_json()

Also puts a decode() call around feed_print() output and adds open()
pragmas to a couple of utilities.

This could still use some tweaking, probably, but it removes a special
case that's bugged me for years and lets the feed code be used for more
general problems.

wrt-ls is a provisional interface to the tools in WRT::EntryStore.  It
should do more, but work is needed that I'm not going to put in before
releasing v5.0.0.

This seems like a good point to call things stable for this major release.
I have a bunch of ideas that I'd like to implement for a v6, which might
well break the API and underlying data structures.

This is all pretty academic since no one else actually uses this thing.

I went and read:

https://pause.perl.org/pause/authenquery?ACTION=pause_namingmodules

Realized I should probably not name this something with an inscrutable
top-level namespace.  WRT is still inscrutable, I guess, but at least
it's now under App.

- Renames all modules, fixes tests (such as they are)
- Zaps old t/validate/ stuff

Now uses:

  wrt display
  wrt render-all
  wrt fcgi