Incorrect SYNOP messages do not lead to raised errors

[RoryPTB]

Invalid SYNOP messages often lead to logged warnings when a decode error should be raised.

For example, when the YYGGiw group is missed, pymetdecoder returns [WARNING] *something* is not a valid code for WindIndicator.

Suggested fix: in __init__.py line 120, add raise DecodeError(str(e)). I have also found raising an error when an invalid section 1 precipitation group is found helps too when section 0 groups are missing, in synop/__init__.py line 176.

[tdbabas]

Hi @RoryPTB - looks like something I originally overlooked! It appears to be a fairly straightforward fix. Will take a look in the New Year