Add optional more aggressive salting (fixes #95)

TEMPLATE.env

@@ -75,4 +75,11 @@ SHOW_SHYNET_VERSION=True
 SHOW_THIRD_PARTY_ICONS=True
 
 # Should Shynet block collection of IP addresses globally?
-BLOCK_ALL_IPS=False
+BLOCK_ALL_IPS=False
+
+# Should Shynet include the date and site ID when hashing users?
+# This will prevent any possibility of cross-site tracking provided
+# that IP collection is also disabled, and external keys (primary
+# keys) aren't supplied. It will also prevent sessions from spanning
+# one day to another.
+AGGRESSIVE_HASH_SALTING=True