Fix issue when the file names contain "temp"

The file selection only scan for the string "temp" in the file names.
This trigger false positive. According to the kernel documentation
for the hwmon sysfs interface, the temperatures *start* with the string
"temp":

 https://www.kernel.org/doc/Documentation/hwmon/sysfs-interface

Using the startswith function on the string solves the issue.

Fixes #5
Add support for historical sensor data

highest() returns the raw highest value
highestc() returns the highest value in Celcius
highestf() returns the highest value in Farenheit

lowest() returns the raw lowest value
lowestc() returns the lowest value in Celcius
lowestf() returns the lowest value in Farenheit

Fixes #2
Add support for min/max temperatures

min() minimum raw temperature
minc() minimum temperature in Celcius
minf() minimum temperature in Fahrenheit

max() maximum raw temperature
maxc() maximum temperature in Celcius
maxf() maximum temperature in Fahrenheit

Fixes #3