feat(tvldb): Import the tvldb/paroxysm source, add a Nix derivation

- This imports the tvldb (actually a thing called 'paroxysm') code
  from https://git.theta.eu.org/eta/paroxysm into the monorepo.
- Additionally, I did a nix thing, yay! \o/
  (well, with tazjin's help)
- 3p/default.nix needed modifying to whitelist pgsql.

Change-Id: Icdf13ca221650dde376f632bd2dd8a087af451bf
Reviewed-on: https://cl.tvl.fyi/c/depot/+/389
Reviewed-by: tazjin <mail@tazj.in>

fun/tvldb/README.md

@@ -0,0 +1,19 @@
+paroxysm
+========
+
+`paroxysm` is a bot for [internet relay chat
+(IRC)](https://en.wikipedia.org/wiki/Internet_Relay_Chat) that lets you store
+small pieces of information, called *factoids*, and retrieve them later. It's
+useful for organising frequently-used information to avoid repeating oneself in
+a busy chatroom, as well as making little todo lists or notes to self in a
+private chatroom.
+
+It was directly inspired by the
+[LearnDB](https://github.com/crawl/sequell/blob/master/docs/learndb.md)
+functionality offered in `##crawl` on chat.freenode.net, and uses similar
+syntax.
+
+## Usage instructions
+
+Will come soon; the project is very much still in beta, and is subject to
+change.