add support for a logger function in errprinter (#681)
add support for a logger function in errprinter (#681)

* add support for a logger function in errprinter

* this enables other software to monkey patch the logger function to capture dronekit output and exceptions

* moved print to stderr to logger function

* monkey patching logger will replace the print to stderr functionality instead of supplement it

dronekit/dronekit-python,diydrones/dronekit-python,hamishwillee/dronekit-python,dronekit/dronekit-python,diydrones/dronekit-python,hamishwillee/dronekit-python