WIP: Generalize properties to constraints

[frenchy64]

Merge first: https://github.com/metosin/malli/pull/1029

In prototyping phase. Overall goal is to obviate the need for :and, :not, and :fn schemas, in particular because of their brittle generators. It also leads more more relevant error messages https://github.com/metosin/malli/issues/1001.

TODO

• [x] validate
• [x] explain
• [x] generate
• [ ] transform
• [x] parse
• [ ] merge/union

Ideas:

• [x] (Noah) allow :or property [:map {:or [:a :b :c]} ..]
• [x] rename :keys to :keyset
• [x] enhance :set with the same properties for heterogeneous sets
• [x] enhance :map-of with keyset constraints
• [x] generalize beyond keysets, just call them "constraints".
• [x] rename :keyset to :and.
• [x] integer constraints [:int {:> 5 :< 10}], easier to generate than [:and :int [:> 5] [:< 10]].
• [x] make :min :max constraints so they can participate in constraint resolution
• [x] extend to :double
• [x] take :gen/min :gen/max into account earlier during solution generation
• [x] perhaps :gen/and :gen/or etc?
• [x] :string constraints
• [x] extend humanize output to structure logical operators explicitly ("should either a or b" => [:or "should a" "should b"])
• [x] :dispatch constraint

[:multi {:dispatch :db/valueType}
 [:db.type/tuple [:map {:xor [:db/tupleType :db/tupleAttrs :db/tupleTypes]}
                  [:db/tupleType {:optional true} ...]
                  [:db/tupleAttrs {:optional true} ...]
                  [:db/tupleTypes {:optional true} ...]]]]
==>
[:map {:dispatch [:db/valueType
                  [:db.type/tuple [:xor :db/tupleType :db/tupleAttrs :db/tupleTypes]]]
                  [:db.type/string ...]
                  [:db.type/ref ...]}
 [:db/tupleType {:optional true} ...]
 [:db/tupleAttrs {:optional true} ...]
 [:db/tupleTypes {:optional true} ...]]