clipping fix, error handling, memory optimizations, ...

[rclasen]

Hi,

as noted in the actual commit messages, this pr is going to fix

• clipping detection in calculateLux
• error handling in various methods
• issues retrieving while the sensor updates it

It's also adding a new stripped down interface that

• is using "way" less memory (36 bytes)
• allows to detect and handle returned errors
• allows more advanced power management

Actually, the old interface was converted into a wrapper for the stripped down one. Unfortunately, the diff became quite big due to this rearrangement.

Rainer

[rclasen]

new interface is still unsatisfying... will rework it.