tests: Add a new solver unit
tests: Add a new solver unit

The Cassowary paper:

  http://constraints.cs.washington.edu/cassowary/cassowary-tr.pdf

has an example of a constrained system:

      2 * x_m = x_l + x_r
     x_l + 10 ≤ x_r
          x_r ≤ 100
            0 ≤ x_l

which can be translated into Constraints as:

    middle == (left + right) / 2 [required]
     right == left + 10          [required]
     right <= 100                [required]
      left >= 0                  [required]

We can add this example to the test suite for the SimplexSolver object,
and verify it.

ebassi/emeus,ebassi/emeus,ebassi/emeus