Fix a bug that import incorrect "non collision group" information from pmx file.
but, this is not a complete fix.
Fix the limits of rigid body constraints.
Add a feature of importing spring settings of pmx file.
Merge branch 'master' into rigids_and_joints
Change "hide rigid body and joints" option to hide joints for spring dynamics.
Add "ignore non collision groups" option.
Update README.md
Improve speed of importing rigid bodies.
Merge branch 'rigids_and_joints' of github.com:sugiany/blender_mmd_tools into rigids_and_joints