- give absolute paths to imgsize() so it chills out on Cwd::getcwd() calls
- rip out App::WRT::MethodSpit's convenience accessors and just access
  elements of $self directly
- kill local_path()
- stop using a() in entry_markup()
- cache get_date_entries_by_depth() results
- swap out state vars for stashing things on $self in
  get_all_source_files()

This gets rendering the whole p1k3 repo back down in the neighborhood of
2.1 seconds, which is a lot more tolerable than 5 or 6.

It also kinda technically breaks the API, maybe, so I guess this'll be a
v5.0.0 after a while.

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

This hadn't been in use for a while anyhow.

It's shorter and the letters are all right there on the keyboard.

Now using File::Basename.