Add ListSchema class

Return it whenever the appropriate Type is converted to a Schema

test/test_schema.py

@@ -0,0 +1,20 @@
+import pytest
+import capnp
+import os
+
+this_dir = os.path.dirname(__file__)
+
+
+@pytest.fixture
+def addressbook():
+    return capnp.load(os.path.join(this_dir, 'addressbook.capnp'))
+
+
+def test_basic_schema(addressbook):
+    assert addressbook.Person.schema.fieldnames[0] == 'id'
+
+def test_list_schema(addressbook):
+    peopleField = addressbook.AddressBook.schema.fields['people']
+    personType = peopleField.schema.elementType
+
+    assert personType.node.id == addressbook.Person.schema.node.id