libsensors: Add support for temp[1-*]_min_hyst and temp[1-*]_lcrit_hyst

Add support for sysfs attributes temp[1-*]_min_hyst (already
implemented by drivers adt7x10, lm77 and lm92) and
temp[1-*]_lcrit_hyst (no known users yet.)
sensors: Add support for temp[1-*]_min_hyst and temp[1-*]_lcrit_hyst
sensors.conf.5: Enhance the hysteresis documentation

Mention all supported temperature hysteresis attributes. Recommend
setting each limit before its hysteresis.