construction from dict cleanup + .py override file support

Diff bb2a01c

The CfgNode constructor can take a dict as an argument that defines that configuration keys and values. However, there were some funky implementation details:

We incorrectly allowed dict as a key value; this shouldn't have been valid because there's no way to tell a nested dict from a CfgNode when serializing and deserializing
If a dict was passed to the constructor, then it could potentially create an invalid CfgNode with nested dict objects as values because it did not recursively convert these to CfgNode objects as done in _to_cfg_node

This diff fixes these issues so that a dict can be provided to the constructor and nested dicts are recursively converted to CfgNode objects.

Diff 68dcec9

Based on feedback, there's a desire to be able to use Python source files to define config overrides. This diff implements the convention that any .py file implementing a module with a cfg attribute of type dict or CfgNode can be used in load_cfg (and hence be used a full config or a config override).

rbgirshick / yacs

construction from dict cleanup + .py override file support #5