Document lua, fix small theme bugs

Lua dev mode functional

Lua support feature-complete

Full implementation of debug mode still pending

lua loading

html.lua functional

Start of Lua support

clippy

Remove ResponseCtx

whitelist -> allowlist

Use http::Response for constructing replies

Add SPDX info to all files

Theming refactor

Theming has been broken off into a seperate space, so that it'll be easier to add lua support later.

Unify import style

Move caching to src/cache/; Finalize API parsing fixes

Font and user cache code has been moved to special files, independant from src/config.rs

API parsing changes have been properly tested, and last.fm API JSON is now trace-logged for debugging convenience.

Reliable user info; Font refactor

Hit a few more endpoints to fix missing images, fallback to default album art just in case.

Refactor the font cache into its own file.

Clippy

Cleanup

Custom font support complete

Add custom font support.

Remove redundant HTML escaping helpers.