DeprecationWarning: inspect.getargspec()

[rosek86]

Hi, thanks for this project, everything works great. I spotted deprecations warning in adxf435xctl, it is recommended to replace inspect.getargspec with inspect.getfullargspec.

./adf435xctl:30: DeprecationWarning: inspect.getargspec() is deprecated since Python 3.0, use inspect.signature() or inspect.getfullargspec()
  calculate_regs_spec = inspect.getargspec(adf435x.calculate_regs)
./adf435xctl:31: DeprecationWarning: inspect.getargspec() is deprecated since Python 3.0, use inspect.signature() or inspect.getfullargspec()
  make_regs_spec = inspect.getargspec(adf435x.make_regs)