Urdf to mjcf (#34)

* update joints.py to match current working version

* early templating for new version of create_mjcf

* get rid of add reference positions since we always do it manually wiht a good pose

* 3.8 version of kol.formats.mjcf since certain typing things incompatible with 3.8 python

* need to keep track of old leg versions for converter to work

* remove some extraneous stuff

* refactor to use robot instead of legs, some improvements for having freejoint, example fixed urdf and xml

* update create fixed torso logic to match pawel's for effort and velocity limits

* refactor some code for create fixed torso

* add keyframe support, swapping right and left legs by default

* lint

* big lint

* remove extra import

.gitignore

@@ -2,7 +2,6 @@
 # Robot Parts
 *.stl
 *.dae
-*.urdf
 # Local files
 .env
 *.DS_Store