Improve code quality

[mbuffa]

Context

Inconsistent API

Main behavior is somewhat inconsistent:

  @callback get(name :: atom()) :: struct() | nil
  @callback set(struct :: struct()) :: {:ok, struct()}
  @callback delete!(name :: atom()) :: {:ok, any()}
  @callback enabled?(name :: atom()) :: boolean()
  @callback enable(name :: atom()) :: {:ok, struct()}
  @callback disable(name :: atom()) :: {:ok, struct()}

• get should probably return {:ok, struct()} to match set return values
• It's quite ok to return just a boolean for enabled?, but we may not need to return anything other than a plain :ok for enable and disable
• delete! should probably drop its exclamation mark. I don't remember why I added it there and not on set (IIRC, I think I dropped it for set)
  • Yup, looks like delete! escaped the slashing: 19d6f6f
• Error specs should probably be added

Code quality

I think code quality could be greatly improved, eg. by:

• Using with when relevant
• Dropping nested cases
• Separating behavior with macro definition
• Making sure errors are correctly checked (|> Type.load() looks sus).