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/api/__init__.py

@@ -20,4 +20,5 @@
 # list of APIs
 APIS = (
     "ldr",
+    "v1",
 )