Add tljh-config command

We do not want users to hand-edit YAML files. This has been a
major source of bugs and confusion for users in z2jh. Doing so
in a terminal text editor makes it even worse.

This lets users type commands directly to modify config.yaml file
rather than edit files directly. This makes it a lot less error
prone and user friendly.

Advanced users can still edit config.yaml manually.

Fixes #38

tests/test_config.py

@@ -0,0 +1,78 @@
+"""
+Test configuration commandline tools
+"""
+from tljh import config
+from contextlib import redirect_stdout
+import io
+import tempfile
+
+
+def test_set_no_mutate():
+    conf = {}
+
+    new_conf = config.set_item_in_config(conf, 'a.b', 'c')
+    assert new_conf['a']['b'] == 'c'
+    assert conf == {}
+
+def test_set_one_level():
+    conf = {}
+
+    new_conf = config.set_item_in_config(conf, 'a', 'b')
+    assert new_conf['a'] == 'b'
+
+def test_set_multi_level():
+    conf = {}
+
+    new_conf = config.set_item_in_config(conf, 'a.b', 'c')
+    new_conf = config.set_item_in_config(new_conf, 'a.d', 'e')
+    new_conf = config.set_item_in_config(new_conf, 'f', 'g')
+    assert new_conf == {
+        'a': {'b': 'c', 'd': 'e'},
+        'f': 'g'
+    }
+
+def test_set_overwrite():
+    """
+    We can overwrite already existing config items.
+
+    This might be surprising destructive behavior to some :D
+    """
+    conf = {
+        'a': 'b'
+    }
+
+    new_conf = config.set_item_in_config(conf, 'a', 'c')
+    assert new_conf == {'a': 'c'}
+
+    new_conf = config.set_item_in_config(new_conf, 'a.b', 'd')
+    assert new_conf == {'a': {'b': 'd'}}
+
+    new_conf = config.set_item_in_config(new_conf, 'a', 'hi')
+    assert new_conf == {'a': 'hi'}
+
+
+def test_show_config():
+    """
+    Test stdout output when showing config
+    """
+    conf = """
+# Just some test YAML
+a:
+  b:
+  - h
+  - 1
+    """.strip()
+
+
+    with tempfile.NamedTemporaryFile() as tmp:
+        tmp.write(conf.encode())
+        tmp.flush()
+
+        out = io.StringIO()
+        with redirect_stdout(out):
+            config.show_config(tmp.name)
+
+    assert out.getvalue().strip() == conf
+
+
+