Draft: Support multiple APIs

This MR implements Support new gwdatafind server APIs (#28) by refactoring gwdatafind.api into a subpackage, and implementing a decorator for the gwdatafind.ui methods that selects the xxx_path function from the right API module dynamically.

Also adds a new -A/--api option for the command-line interface.

gwdatafind/tests/test_main.py

@@ -121,9 +121,12 @@ def test_sanity_check_fail(clargs):
         parser.parse_args(clargs)
 
 
-@mock.patch("gwdatafind.ui.ping")
-def test_ping(mping):
+def test_ping(requests_mock):
     """Test `ping()."""
+    requests_mock.get(
+        "https://test.datafind.com:443/api/version",
+        json={"version": "1.2.3"},
+    )
     args = argparse.Namespace(
         server="test.datafind.com:443",
         api="v1",
@@ -131,14 +134,10 @@ def test_ping(mping):
     )
     out = StringIO()
     main.ping(args, out)
-    mping.assert_called_with(
-        host=args.server,
-        api=args.api,
-        ext=args.extension,
-    )
     out.seek(0)
     assert out.read().rstrip() == (
-        "LDRDataFindServer at test.datafind.com:443 is alive")
+        "GWDataFind Server v1.2.3 at test.datafind.com:443 is alive"
+    )
 
 
 @mock.patch("gwdatafind.ui.find_observatories")