update docstrings and random cleanups (#387)

* fixing docstrings and small nits; up to fileds

* finished adding and fixing docstrings

docs/reference/api/config.rst

@@ -0,0 +1,8 @@
+.. _configs:
+
+Configs
+============
+
+.. automodule:: nerfactory.configs.base
+   :members:
+   :show-inheritance:

docs/reference/api/index.rst

@@ -7,6 +7,7 @@ TODO: Explanation of each component
 
 .. toctree::
 
+    config
     data
     fields
     fields/modules/index