Adding allowMultiple field to Parameter

According to Swagger spec it should be possible to list parameter's values.
See https://github.com/wordnik/swagger-spec/blob/master/versions/1.2.md#524-parameter-object

If one generates swagger json from code right now there is a warning:
````
[INFO] Skipping unsupported property: "allowMultiple" for @Swagger\Annotations\Parameter, expecting "paramType", "name", "type", "required", "description", "format", "items", "uniqueItems", "minimum", "maximum", "enum", "defaultValue", "_partialId", "_partials", "_context" in 
````
Adding this public field to Parameter's Annotation solves this issue. Generated client application (using swagger-ui) works fine.