v2.2.0 — merge several sources, AniList tags, and one collection per genre

Three changes to what ends up written on a title, all from a library in use. Upgrading
is a pull: the defaults are the old behaviour, and no cached item is invalidated by the
upgrade itself.

Several sources at once, not just one after another

providers has always been a preference order. providerMode now says what that order
means:

Mode	What a title costs	What it returns
fallback (default, and what 2.1 did)	one request, until a source answers	the first answer
merge	one request per source	every source's genres, pooled

{ "library": "Animes", "type": "anime",
  "providers": ["jikan", "anilist", "tmdb"], "providerMode": "merge",
  "overrides": { "maxGenres": 10 } }

In the console it is a switch under the source presets, and with it on, the TMDB
fallback reads "…and TMDB" rather than "…then TMDB", because that is what it now does.

Merging is worth a cap — three sources can hand back thirty names for one title. One
rule is worth knowing: a title you bound by hand is only asked of the sources that can
read the id you pinned. The others would search by title and merge back the very match
the binding exists to override.

Keywords are a property of the source, not of the library type

useKeywords meant TMDB's keywords. AniList's community tags are the same idea, and
its genre list is a dozen broad buckets that say little across a whole library. AniList
now returns its tags instead of those genres when keywords are asked for, still
filtered to high-agreement, non-spoiler tags.

So the rule is no longer about the library type: useKeywords needs a source that has
keywords — TMDB or AniList — and the error says which sources the library actually
reads. MyAnimeList has none, its themes and demographics being part of the genres it
returns already.

One genre, one collection

Two sources spell one idea differently and Plex grows two collections: Boys Love
beside Boys' Love. Genre names are now compared on letters and digits alone, so
case, accents, punctuation and spacing stop splitting a genre in two. The first
spelling a source returned is the one written, and a rename rule reaches every spelling
of its key — one "sci fi" line catches Sci-Fi, SciFi and sci fi.

Words that genuinely differ cannot be guessed, so a localized source beside
English-only ones still needs a line each:

"defaults": { "anime": { "replace": { "comedie": "Comedy" } } }

One line covers Comédie, comedie and COMÉDIE. The other way out is to stop the
mismatch at the source: TMDB_LANGUAGE=en-US makes TMDB agree with MyAnimeList and
AniList, which are English-only.

Items already in the cache keep the tags they have — the upgrade deliberately does not
invalidate them. To re-tag a library with the folding applied, run it once with
--force; collections left empty afterwards are Plex's to tidy.