Revisit the idea of hooks

[mattmc3]

Similar to running zsh-defer to load plugins, antidote should support antidote-source (via a separate plugin hosted at https://getantidote) as a means to add add hooks (https://github.com/zsh-hooks/zsh-hooks).

Hooks would allow us to add 'loaded' indicators in zstyles, check installs, etc. It's a better way to do things than pre:/post: annotations.

• Note: possibly deprecate pre/post