Merge pull request #3 from maksim-kozich/master

update lib "url" version

0.3.4: export JsMap,JsNumber,JsError

0.3.2: JsonSchema: fix serialization/deserialization of the required-…

…attribute of object-node

0.3.1: SchemaCompiled impl std::fmt::Debug

0.3.0: use valico's ScopedSchema properly

0.2.7: if object schema has no properties — treat it as a Map, i.e. p…

…reserve all properties upon coercion

0.2.6: coercion of an object always enumerates the fields explicitly

0.2.5: SchemaNode::for_literal(&JsValue) for object literals

0.2.4: Coercion::is_subtyping_only(&self) -> bool

0.2.3: Schema and JsValue coercions are implemented