I never could quite figure out why non-ASCII characters were getting
badly munged in XML::Atom::SimpleFeed output.  Using Encode::decode() on
the content of entries turns out to fix this, although it's probably the
tip of an iceberg.

- get_all_source_files() -> EntryStore::all()
  - get_date_entries_by_depth() -> EntryStore::dates_by_depth()
  - get_recent_entries_by_depth() -> EntryStore::recent_by_depth()

...plus some convenience methods for accessing recent or all years /
months / days, and a next($entry) / previous($entry) for indexing into the
date lists.

An instance of App::WRT::EntryStore is stashed on an App::WRT instance.

Replaces get_all_day_entries() with get_date_entries_by_depth().  Adds
generate_month_lists() to stash %prev_months and %next_months (this can
probably be generalized a bunch).

Generalizes sortable_date_from_entry() to work with different levels of
date.  Assumes that no component of the date is more than 4 digits, which
is not very future proof.  (Though if this code is still running in the
year 10000, the future will have gone very differently than I expect it
to.)

month_before() now uses the %prev_months and %next_months hashes.

Removes fulltext(), because you can just call get_date_entries_by_depth(3).

Much slower than it probably needs to be.

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.

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

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

This whole sub is gross.

- strip HTML::Defang
- get rid of old wala markup code
- use Discount for both markup modules (with NOHTML flag in wala)

...also test that it'll render a snippet.