Fastjsonschema

* Fix of `additionalProperties=true` for JSON schema 4
* Use decimal for multipleOf implementation and add respective tests
* Better escaping of definition names

* Fix of undefined format exception message

* Optimization: do not do the same type checks, keep it in one block if possible
* More context in JsonSchemaException (value, variable_name, variable_path, definition, rule and rule_definition)
* Possibility to pass custom formats
* Raise JsonSchemaDefinitionException when definition of property is not valid
* Fix of uniqueItems when used with other than array type
* Fix of date-time regexp (time zone is required by RFC 3339)

* Resolved Python 3.7 warnings
* Updated JSON Schema test suites
* Fix of date-time regexp (allow small T and Z).
* Fix escaping (proper handling of \n, \r or " everywhere).

* Fix of properties (local variable referenced before assignment).

* Fix of additionalProperties (colliding variable names).