Convert get_parameter_max to capitalize on map data structure.

Also add an assert to get_parameter_min to ensure the first segment
starts at the start of the piecewise curve.

It will most likely be appropriate to remove explicit t0 from the curve
and always use the parameter of the first curve instead.
Convert find_segment to use the fast lookup provided by the map container.

This conversion yields the primary benefit of using a map container for
piecewise curves.

A number of safety checks were added to ensure proper behavior.  Some of
these checks are most likely redundant and should be removed as this
conversion evolves.

The tolerance on one of the test cases was increased such that it would
pass.
Improve set_t0