Reimplement FastPiecewise.limit in terms of new method FastPiecewise.limits
Improve plotting of discontinuity markers for testcase h = FastPiecewise([[singleton_interval(0), FastLinearFunction(0,0)], [open_interval(0, 1/2), FastLinearFunction(6, -1)], [closed_interval(1/2,1), FastLinearFunction(-2, 2)]], merge=False)
Merge branch 'discontinuous_piecewise' of https://github.com/mkoeppe/infinite-group-relaxation-code into discontinuous_piecewise

Conflicts:
	functions.sage