URI parsing decorator (#613)

- array logic refactored into one place.
- validation.py and parameter.py no longer try to join the array, and the split it again.
- validation of defaults now works, because the validator is given the correct type.
- some additional classes that change the behavior of deduplicating query parameters that are defined multiple times
  - **AlwaysMultiURIParser** that is backwards compatible, warts and all (used by default)
  - **Swagger2URIParser** that adheres to the spec's definition of `collectionFormat: multi` and uses the last-defined query parameter value (ex. `query?a=1&a=2` => `a = 2`)
  - **FirstValueURIParser** that behaves like Swagger2URIParser, except that the first-defined value is used (ex. `query?a=1&a=2` => `a=1`)

tests/api/test_parameters.py

@@ -42,6 +42,10 @@ def test_required_query_param(simple_app):
 def test_array_query_param(simple_app):
     app_client = simple_app.app.test_client()
     headers = {'Content-type': 'application/json'}
+    url = '/v1.0/test_array_csv_query_param'
+    response = app_client.get(url, headers=headers)
+    array_response = json.loads(response.data.decode('utf-8', 'replace'))  # type: [str]
+    assert array_response == ['squash', 'banana']
     url = '/v1.0/test_array_csv_query_param?items=one,two,three'
     response = app_client.get(url, headers=headers)
     array_response = json.loads(response.data.decode('utf-8', 'replace'))  # type: [str]