Preserve individual headers with the same name on responses (#1208)

* Preserve individual headers with the same name on responses

* Rename RequestHeadersDict to HTTPHeadersDict

* Update tests/utils/http_server.py

* Update tests/utils/http_server.py

* Update httpie/adapters.py

Co-authored-by: Jakub Roztocil <jakub@roztocil.co>

httpie/cli/dicts.py

@@ -9,7 +9,7 @@ class BaseMultiDict(MultiDict):
     """
 
 
-class RequestHeadersDict(CIMultiDict, BaseMultiDict):
+class HTTPHeadersDict(CIMultiDict, BaseMultiDict):
     """
     Headers are case-insensitive and multiple values are supported
     through the `add()` API.

httpie/cli/requestitems.py

@@ -11,7 +11,7 @@ from .constants import (
 )
 from .dicts import (
     BaseMultiDict, MultipartRequestDataDict, RequestDataDict,
-    RequestFilesDict, RequestHeadersDict, RequestJSONDataDict,
+    RequestFilesDict, HTTPHeadersDict, RequestJSONDataDict,
     RequestQueryParamsDict,
 )
 from .exceptions import ParseError
@@ -21,7 +21,7 @@ from ..utils import get_content_type, load_json_preserve_order_and_dupe_keys
 class RequestItems:
 
     def __init__(self, as_form=False):
-        self.headers = RequestHeadersDict()
+        self.headers = HTTPHeadersDict()
         self.data = RequestDataDict() if as_form else RequestJSONDataDict()
         self.files = RequestFilesDict()
         self.params = RequestQueryParamsDict()