Add support for the Kumar Lab's JABS format (#63)

* Adding read functions for jabs pose files

* Figured out track and adding function into init

* pose_v3 export mostly working. Adding some structure for other pose versions

* Bugfix on sorting out tracks

* Adding in writing out JABS pose versions

* Fixing a pose_v4 field and beginning to address some todos

* updating todos

* Adding static object support

* Cleanup of todos and removing some unused variables when writing h5 files

* Ran black

* conforming to linter

* pep8 linting

* Tentative solution for jabs v3 complaince. Needs testing...

* Starting to write some tests

* Making tests actually correct and fixing a bug discovered with the a test!

* Adding tests for reading/writing jabs files from main

* Enforcing 12 keypoints with a warning. Removing an unecessary check (all Instances have skeletons)

* Being more explicit with some checks. One bugfix with reading v2 files.

* Bot caught this one - checks were in correct order, but raised errors were not.

sleap_io/__init__.py

@@ -22,4 +22,6 @@
     save_nwb,
     load_labelstudio,
     save_labelstudio,
+    load_jabs,
+    save_jabs,
 )