Sort by feed article length

[jbenge1]

Fixes #177 Sort by article content length (respects read/unread ordering still)

• ordering: length
  • New value "length" settable in config.
• unread-first still trumps length
• sort-toggle key noops in length mode
  • Switched checking to use switch statement instead of if else if
  • Explicitly checking against Asc/Desc and default noops (Though I'm happy to have it cycle through the three ordering options if that's preferred)
  • unknown ordering values no longer coerce to asc on toggle — they noop
• Added two tests for store.go to verify existing functionality and new functionality

Tested: go test ./... (note: TestNewDefaultWithXDGConfigHome fails on macOS regardless of this change, I'm happy to file a bug separately if folks think it's necessary), plus manual TUI verification against direct sqlite queries.

[guyfedwards]

Awesome, thanks @jbenge1. If you could file the bug for the mac test failure that would be great thanks

[guyfedwards]

Released in https://github.com/guyfedwards/nom/releases/tag/v3.3.2