Checkpoint first thrust of map gen features.

Complex keys are a behemoth of a feature, and it's gonna take
substantial effort to sort all of that out.

schema/tmpBuilders.go

@@ -28,10 +28,15 @@ func SpawnLink(name TypeName) TypeLink {
 func SpawnLinkReference(name TypeName, referenceType Type) TypeLink {
 	return TypeLink{anyType{name, nil}, referenceType, true}
 }
+
 func SpawnList(name TypeName, typ Type, nullable bool) TypeList {
 	return TypeList{anyType{name, nil}, false, typ, nullable}
 }
 
+func SpawnMap(name TypeName, keyType Type, valueType Type, nullable bool) TypeMap {
+	return TypeMap{anyType{name, nil}, false, keyType, valueType, nullable}
+}
+
 func SpawnStruct(name TypeName, fields []StructField, repr StructRepresentation) TypeStruct {
 	v := TypeStruct{
 		anyType{name, nil},