TargetThermostatMode and ThermostatMode erroneously assumed equivalent

[timcharper]

TargetThermostatMode is described by the following enums:

• 0 - Off
• 1 - Heat
• 2 - Cool
• 3 - Auto

(See https://github.com/KhaosT/HAP-NodeJS/blob/master/lib/gen/HomeKitTypes.js#L2342)

CurrentThermostatMode is described by a similar, but reduced, set of values:

• 0 - Off
• 1 - Heat
• 2 - Cool

(See https://github.com/KhaosT/HAP-NodeJS/blob/master/lib/gen/HomeKitTypes.js#L555)

It would be illegal for a thermostat to report itself as currently "autoing" the house, per the spec.

[timcharper]

@beowulfe #62 is the fix which takes the approach you suggested, and preserved backwards compatibility