Add support for request.get's 'params' param (#770)

* Add support for request.get's 'params' param

Requests defines the following API:
`get(url, params=None, **kwargs)`

* Improve typing for requests.get(params)

Add support for string form, and tighten restrictions for the dict form
to allow only string keys/vals. Technically, anything is allowed since
the code (I guess) runs `str(key)` and `str(value)`, but it seems better
to keep the stub somewhat strict so it can help pick up potential
errors.

third_party/2/requests/api.pyi

@@ -1,11 +1,17 @@
 # Stubs for requests.api (Python 3)
 
-from typing import Union
+from typing import Union, Optional, AnyStr
 
 from .models import Response
 
 def request(method: str, url: str, **kwargs) -> Response: ...
-def get(url: Union[str, unicode], **kwargs) -> Response: ...
+
+def get(url: Union[str, unicode],
+        params: Optional[Union[dict[Union[str, unicode],
+                                    Union[str, unicode]],
+                               Union[str, unicode]]]=None,
+        **kwargs) -> Response: ...
+
 def options(url: Union[str, unicode], **kwargs) -> Response: ...
 def head(url: Union[str, unicode], **kwargs) -> Response: ...
 def post(url: Union[str, unicode], data=..., json=...,

third_party/3/requests/api.pyi

@@ -1,11 +1,15 @@
 # Stubs for requests.api (Python 3)
 
-import typing
+from typing import Optional, Union, Any
 
 from .models import Response
 
 def request(method: str, url: str, **kwargs) -> Response: ...
-def get(url: str, **kwargs) -> Response: ...
+def get(url: Union[str, bytes],
+        params: Optional[Union[str,
+                               bytes,
+                               dict[Union[str, bytes], Union[str, bytes]]]]=None,
+        **kwargs) -> Response: ...
 def options(url: str, **kwargs) -> Response: ...
 def head(url: str, **kwargs) -> Response: ...
 def post(url: str, data=..., json=..., **kwargs) -> Response: ...