change api.supports_hash to take a hash class rather than a str

* This change means hash class names will be byte strings and we no
  longer need to encode to ascii on hashobject.name in
  create_hash_context
diff --git a/tests/primitives/test_hashes.py b/tests/primitives/test_hashes.py
index 1bc2e9e..4ad5c89 100644
--- a/tests/primitives/test_hashes.py
+++ b/tests/primitives/test_hashes.py
@@ -23,6 +23,6 @@
         hashes.SHA1,
         digest_size=20,
         block_size=64,
-        only_if=lambda api: api.supports_hash("sha1"),
+        only_if=lambda api: api.supports_hash(hashes.SHA1),
         skip_message="Does not support SHA1",
     )