model.simulate: set plot dpi to 150
teensy/controller.c: change controller_heater to take s (was ms)
model.simulate: fix arguments to C controller

The controller now takes seconds instead of ms.
teensy/controller.c: renamed to controller.cpp
teensy/main.cpp: use the new controller
teensy/version.h: bump version to 2
model.simulate: add comment to Controller base class
model.simulate: add T2 to the base Controller

T2 (the second bimetallic thermostat) disconnects the power
to the heater at T == 140.
util: add some utilities
teensy/main.cpp: fix test setup
teensy/version.h: bump to version 3