build in temperature ramping

[mphendricks]

This would follow up issue #21 and would accept a start temperature, final temperature, and time, and then translate this one line to a number of lines (10? depends on temp difference or time?) with intermediate temperatures and pause steps in between them.

For example:
temp_ramp(T_init = 25, T_final = 80, time = 9) would be translated to:

temp_on(30 C)
pause(60 sec)
temp_on(35 C)
pause(60 sec)
temp_on(40 C)
pause(60 sec)
temp_on(45 C)
pause(60 sec)
temp_on(50 C)
pause(60 sec)
temp_on(55 C)
pause(60 sec)
temp_on(60 C)
pause(60 sec)
temp_on(65 C)
pause(60 sec)
temp_on(70 C)
pause(60 sec)
temp_on(75 C)
pause(60 sec)
temp_on(80 C)

Note that this wouldn't be exact because it ignores the actual heating/cooling time for the temperature controller, but as long as the time is reasonably long then this probably won't be significant, and if there are enough intermediate points then it won't take it long to get between them. Maybe there's a better way to track time and handle this, but I think this would cover our needs.