prepare_connection plugin hook

Closes:
- #574

Refs #567

---------

Co-authored-by: Simon Willison <swillison@gmail.com>

sqlite_utils/hookspecs.py

@@ -8,3 +8,8 @@ hookimpl = HookimplMarker("sqlite_utils")
 @hookspec
 def register_commands(cli):
     """Register additional CLI commands, e.g. 'sqlite-utils mycommand ...'"""
+
+
+@hookspec
+def prepare_connection(conn):
+    """Modify SQLite connection in some way e.g. register custom SQL functions"""