Add power figures, cleanup output format

- Changed naming of 'PSU' and 'Load' voltages to 'VIN+' and 'VIN-' as I initially thought 'PSU' was referring to I2C logic level Vcc. Not sure why previous names were chosen, I can't find any IN219 eval boards that don't used VIN+/VIN-.
- Added power figures both from on chip register (lower resolution) as well as one calculated in Python using the full resolution voltage/current values
- Align output in columns with correct significant figures

Author: WizardTim

examples/ina219_simpletest.py

@@ -31,12 +31,15 @@
     bus_voltage = ina219.bus_voltage  # voltage on V- (load side)
     shunt_voltage = ina219.shunt_voltage  # voltage between V+ and V- across the shunt
     current = ina219.current  # current in mA
+    power = ina219.power  # power in watts
 
     # INA219 measure bus voltage on the load side. So PSU voltage = bus_voltage + shunt_voltage
-    print("PSU Voltage:   {:6.3f} V".format(bus_voltage + shunt_voltage))
-    print("Shunt Voltage: {:9.6f} V".format(shunt_voltage))
-    print("Load Voltage:  {:6.3f} V".format(bus_voltage))
-    print("Current:       {:9.6f} A".format(current / 1000))
+    print("Voltage (VIN+) : {:6.3f}   V".format(bus_voltage + shunt_voltage))
+    print("Voltage (VIN-) : {:6.3f}   V".format(bus_voltage))
+    print("Shunt Voltage  : {:8.5f} V".format(shunt_voltage))
+    print("Shunt Current  : {:7.4f}  A".format(current / 1000))
+    print("Power Calc.    : {:8.5f} W".format(bus_voltage*(current/1000)))
+    print("Power Register : {:6.3f}   W".format(power))
     print("")
 
     time.sleep(2)