Allow body on HTTP DELETE view methods (#122)

* Allow body in delete requests
* Do not add request body to DELETE by default
* Check manual form parameters against body_methods
* Add tests
* Add changelog

Closes #118

src/drf_yasg/inspectors/base.py

@@ -276,7 +276,10 @@ class SerializerInspector(FieldInspector):
 
 
 class ViewInspector(BaseInspector):
-    body_methods = ('PUT', 'PATCH', 'POST')  #: methods that are allowed to have a request body
+    body_methods = ('PUT', 'PATCH', 'POST', 'DELETE')  #: methods that are allowed to have a request body
+
+    #: methods that are assumed to require a request body determined by the view's ``serializer_class``
+    implicit_body_methods = ('PUT', 'PATCH', 'POST')
 
     # real values set in __init__ to prevent import errors
     field_inspectors = []  #: