Investigate whether a HX711 can be detected

[endail]

Reading from an unconnected GPIO could lead to the process hanging (or another other unpredictable result). It may be of some use to have a method of the HX711 class to "test" whether a HX711 could be detected by using a simple read which times-out after some predefined time. Conversely, it may even be better to implement a configurable timeout within the isReady and readValue methods.