change field-spec-of to force 'type' and allow entity-or-type as argu…

…ment

This change is needed for references.  When using get-reference, grab, grab-in
you pass the entity and those functions use 'field-spec-of' to get the correct document.
'field-spec-of' returned nil because entity was being sent not type.

src/karras/entity.clj

@@ -139,10 +139,11 @@ Example:
     (class entity-or-type)))
 
 (defn field-spec-of
-  "Given a type and one or more keys,
+  "Given a type or entity  and one or more keys,
    returns the  field spec for the last key."
-  [type & keys]
-  (let [field-type (or (reduce (fn [t k]
+  [entity-or-type & keys]
+  (let [type (get-type entity-or-type)
+        field-type (or (reduce (fn [t k]
                                  (-> t entity-spec :fields k :type))
                                type
                                (butlast keys))