getVertices

Calculate vertices of feasible set given linear constraints (R^2).

This function computes:
(a) the set of vertices of the R^2 polygon defined by the linear
constraints in ['dirs', 'levels'], and
(b) a boolean (logical) vector of which constraints are binding.
The function only works for R^2. If the linear constraints define the
empty set, an error is triggered.

Inputs:
* 'dirs' an [n,2] sized matrix, where dirs(i,:) are linear
constraint coefficients.
* 'levels' an [n,1] sized matrix where x=[x1,x2] must satisfy
dot(dirs(i,:),x) <= levels(i).
* 'isSorted' boolean for whether the constraints are sorted by
angle (in either direction).

Outputs:
* 'V' the set of vertices of the feasible region defined by the
input linear constraints.
* 'binding' [optional] an [n] sized vector which has '1' if the
constraints [dirs(i)*x <= levels(i)] is binding, '0' otherwise.