libinithooks updates

[JedMeister]

• Add inithooks_log library
• libinithooks styling updates (black)
• inithooks_cache changes:
  • support setting cache dir at Keystore class initialisation - not just via env var
  • support providing fallback value for read()

turnkeylinux-apps/nextcloud#28 depends on this

[JedMeister]

In discussion with @OnGle regarding the changes to inithooks_cache, he noted that I've changed the default behaviour of .read().

When calling read(), my changes added support for proving a fallback value - which would be returned if the key does not exist in the cache. My idea was based on the behavior of os.environ when getting an env var.

However with my changes, if a cached value does not exist and no fallback is given, an empty string is returned. Previously None would be returned.

While I think that returning an empty string would be preferable (particularly for typing), @OnGle's point was that the change may have unintended negative consequences in existing uses of inithooks_cache elsewhere. I think that's fair.