Add ability to import modules with dashes or spaces

Any module with underscores in it will now attempt to look for 3 files,
first the original, then with dashes, then with spaces, ie:
import addressbook_v_2_capnp
will search for 'addressbook_v_2.capnp', 'addressbook-v-2.capnp', and
'addressbook v 2.capnp'.

test/test_load.py

@@ -58,6 +58,12 @@ def test_failed_import():
 def test_defualt_import_hook():
     import addressbook_capnp
 
+def test_dash_import():
+    import addressbook_with_dashes_capnp
+
+def test_spaces_import():
+    import addressbook_with_spaces_capnp
+
 def test_add_import_hook():
     capnp.add_import_hook([this_dir])