added versioning headers to the API

src/paperless/middleware.py

@@ -0,0 +1,18 @@
+from django.conf import settings
+
+from paperless import version
+
+
+class ApiVersionMiddleware:
+
+    def __init__(self, get_response):
+        self.get_response = get_response
+
+    def __call__(self, request):
+        response = self.get_response(request)
+        if request.user.is_authenticated:
+            versions = settings.REST_FRAMEWORK['ALLOWED_VERSIONS']
+            response['X-Api-Version'] = versions[len(versions)-1]
+            response['X-Version'] = ".".join([str(_) for _ in version.__version__])
+
+        return response