Don't overrun reflow profile array

This also solves the problem that the reflow cycle runs one 10-second
period too many, incorrectly ramping down to zero.
Remove unused profile buffer
Use define for number of temp setpoints per profile
Adjust minimum profile temperature
Add an optional Ramp speed test profile
Only force-cool down to 50C

Also make sure fan stops running when oven temperature is below standby
temperature
More PID adjustments
Add optional max temp override

Instead of only relying on the average of the first two TC channels for
regulation, use the maximum temperature detected by any TC if it is 5C
above the average.
Fix typo
Merge pull request #32 from UnifiedEngineering/reflow-fixes

Reflow fixes