Add an outer loop in mbpfan.c:retrieve_sensors to loop over all coretemp
directories. Also increase hard-coded limits from 10 to 12 or 16 since
the temp endpoints are sometimes indexed that high.
For example, this is required for supporting a Mac Pro with two processors
of 16 cores, requiring
/sys/devices/platform/coretemp.0/hwmon/hwmon0/temp{1..12}
/sys/devices/platform/coretemp.1/hwmon/hwmon1/temp{1..12}
Fixes#152.
