Refactored modules related to input-output (#194)

* added from_numpy() function to the load_poses module

* unit test new function

* use from_numpy() function in other loaders as well

* add Examples section to docstring and render in API index

* add Examples section to docstring and render in API index

* confidence array is optional

* None is the default for confidence

* rename private functions

* renamef from_dlc_df to from_dlc_style_df

* harmonise docstrings in load_poses

* harmonised function names and docstrings in save_poses

* harmonised docstrings in validators

* split Input/Output section of API index into modules

* renamed `_from_lp_or_dlc_file` to `_ds_from_lp_or_dlc_file`

docs/source/api_index.rst

@@ -4,27 +4,33 @@ API Reference
 =============
 
 
-Input/Output
-------------
+Load poses
+----------
 .. currentmodule:: movement.io.load_poses
 .. autosummary::
     :toctree: api
 
+    from_numpy
     from_file
     from_sleap_file
     from_dlc_file
-    from_dlc_df
     from_lp_file
+    from_dlc_style_df
+
+Save poses
+----------
 
 .. currentmodule:: movement.io.save_poses
 .. autosummary::
     :toctree: api
 
     to_dlc_file
-    to_dlc_df
-    to_sleap_analysis_file
     to_lp_file
+    to_sleap_analysis_file
+    to_dlc_style_df
 
+Validators
+----------
 .. currentmodule:: movement.io.validators
 .. autosummary::
     :toctree: api
@@ -58,7 +64,7 @@ Filtering
 
 
 Analysis
------------
+--------
 .. currentmodule:: movement.analysis.kinematics
 .. autosummary::
     :toctree: api