SSMTool 2.0: Computation of invariant manifolds in high-dimensional mechanics problems

In this pre-release version, we demonstrate the computational methodology over limited examples.

This package uses the following external open-source packages:

1. Continuation core (coco) https://sourceforge.net/projects/cocotools/
2. Sandia tensor toolbox: https://gitlab.com/tensors/tensor_toolbox
3. Combinator: https://www.mathworks.com/matlabcentral/fileexchange/24325-combinator-combinations-and-permutations