consolidate yaml configuration

workaround ruamel.yaml issue 255,
where once an empty dict or list has been written,
'flow' style is used thereafter, using dense `{key: value}` form
instead of traditional yaml block style.

tests/test_yaml.py

@@ -0,0 +1,19 @@
+from tljh.yaml import yaml
+
+
+def test_no_empty_flow(tmpdir):
+    path = tmpdir.join("config.yaml")
+    with path.open("w") as f:
+        f.write("{}")
+    # load empty config file
+    with path.open("r") as f:
+        config = yaml.load(f)
+    # set a value
+    config["key"] = "value"
+    # write to a file
+    with path.open("w") as f:
+        yaml.dump(config, f)
+    # verify that it didn't use compact '{}' flow-style
+    with path.open("r") as f:
+        content = f.read()
+    assert content.strip() == "key: value"