Eliminate possibility of heat and cool relays being active simulateneously.

Previously each method turned on the relays it needed and left the other
methods untouched. This leaves open the possibility of heat and cool being
active at the same time. For example: Thermostat is in heat mode (heat and
fan relays active), program is stopped. Start program and go into cool
mode (cool and fan active). Heat is never turned off, all relays active.

Each method now turns off any unused relays.
Reads temperature sensor via lm-sensors

Previously read temperature from stdin for manual testing purposes. Now
uses linux lm-sensors package command `sensors -f` and awk to get
temperature.
Adjusts differential and set points

3 degree differential was too much, 2 is more comfortale.
Cooling won't be needed for a few weeks, set the cool setpoint to
99. This will be put to a more reasonable temp once more testing
has been done.
Sets timeouts to reasonable levels

Timeouts were set low for testing purposes. Fan timeout is set to 15
seconds and the heat-to-cool/cool-to-heat timeout is set to 5 minutes.