Adding sample collection code

Adjusted get_temp() to poll until NaN is false. Adding math.h
library. Adding functions to calculate mean and standard deviation of an
array of data. Changed initialization of doubles to 0.0. Function
add_sample() will add a sample to the samples collection if it is not
outside our margin of error (currently either less than 10, more than
500, or more than 5 standard deviations away from the mean), otherwise
it repeats the prior sample as filler. In loop(), internal_temp is
calculated as the mean of the samples. In setup(), the samples array is
filled with current temperature data.
Adding time button

When pressed, adds ten seconds to the roast time
Bug fixes

Initial states set to COUNT so initial call to idle() functions executes
properly. get_temp() fixed with a do while so it reads until no
error. No longer prints individual temps. Fixing setup() so that SD card
error doesn't exit function, just sets log flag to false.
Fixing calculate() functions, sending them SIZE

Getting size of array wasn't working, now just sending a size since we
have it (SAMPLE_SIZE).
Changing pin numbers

Makes more sense now, plus had to give up 11-13
Fixing SD Card initialization and log file writing