Brevo: SendinBlue compatibility

(See previous commit.)

- Maintain deprecated compatibility
  versions on the old names/URLs.
  (Split into separate commit
  to make renamed files more
  obvious.)

anymail/backends/sendinblue.py

@@ -0,0 +1,20 @@
+import warnings
+
+from ..exceptions import AnymailDeprecationWarning
+from .brevo import EmailBackend as BrevoEmailBackend
+
+
+class EmailBackend(BrevoEmailBackend):
+    """
+    Deprecated compatibility backend for old Brevo name "SendinBlue".
+    """
+
+    esp_name = "SendinBlue"
+
+    def __init__(self, **kwargs):
+        warnings.warn(
+            "`anymail.backends.sendinblue.EmailBackend` has been renamed"
+            " `anymail.backends.brevo.EmailBackend`.",
+            AnymailDeprecationWarning,
+        )
+        super().__init__(**kwargs)