Clojurians Log v2

@eoliphant the first alpha wanted to be immutable by default. We could revisit that for 1.0.0, starting to think it would be ok if malli was optionally immutable: the JVM/compiler option could be to close things up.

when one does multi-tenant schema systems, anyway the registry is either local or passed as option -> one can have already full control of the registries in places where it matters. The system default registry is just for your own core app, not the tenants.

maybe have a up-to-date branch of malli with the option reversed?

also, comments welcome on having an optional global registry. Something like (malli.mutable/register! :user/name :string)