Issue #16473: Fix byte transform codec documentation; test quotetabs=True

This changes the equivalent functions listed for the Base-64, hex and Quoted-
Printable codecs to reflect the functions actually used. Also mention and
test the "quotetabs" setting for Quoted-Printable encoding.
diff --git a/Lib/encodings/quopri_codec.py b/Lib/encodings/quopri_codec.py
index f259149..e4965da 100644
--- a/Lib/encodings/quopri_codec.py
+++ b/Lib/encodings/quopri_codec.py
@@ -21,7 +21,7 @@
     # using str() because of cStringIO's Unicode undesired Unicode behavior.
     f = StringIO(str(input))
     g = StringIO()
-    quopri.encode(f, g, 1)
+    quopri.encode(f, g, quotetabs=True)
     output = g.getvalue()
     return (output, len(input))