Shuffles a bit of stuff out of App::WRT::Renderer into App::WRT, including
the method now called get_all_source_files() and a new one called
get_all_day_entries() that returns a sorted listed of days.

Uses state variables to cache the get_all_source_files() data, as well
as month_before() data (this was previously memoized inside a closure).

App::WRT::feed_print() now takes a list of entries instead of a month to
render the feed for.

App::WRT::feed_print_latest() gets a feed with most recent feed_length
entries.

It's weird to have this hardcoded, and there's
context on each entry anyway.

The default was `$0?`, which I think was probably a holdover from this
being invoked as a CGI script.  `$0` would give the name of the current
script, so you'd wind up with `display.cgi?2008` or what-have-you.

Adds a wrt-init kind of on the model of git init for starting a stub
directory with wrt.json, archives/, publish/, and templates/.

Also starts to tweak POD a bit.

This is based on a recommendation from CPANTS:

https://cpants.cpanauthors.org/release/BRENNEN/App-WRT-v4.0.1

> Add a 'repository' resource to the META.yml via 'meta_add' accessor
> (for Module::Build) or META_ADD parameter (for ExtUtils::MakeMaker).

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.

- create an index.html with new entries
- create an /all/index.html with a list of all entries
- create a /feed containing an atom feed of the most recent month
- a paragraph on requirements in the installation section
- copyright date through 2017

I never did get around to writing one of these.  At this point in history,
I guess I don't regret the omission.

This will probably eventually bite me, since it could overlap with other
entry display logic, but it doesn't seem to break anything at the moment.

This is a fairly p1k3-specific thing.