[Enhancement] Add Path.Compound Static Method

[jonobr1]

Describe the feature you'd like
Create a static method on Two.Path to be able to combine any number different paths and return a new compound path.

const compound = Two.Path.compound(a, b, c, d);

Functionally the code would project every vertex and concatenate them together into one list of vertices.

Additional context
Related to the Boolean Operations issue: #596