be liberal with extra commas

[jmettraux]

#76 (comment)

The other common input that changed is a trailing comma, like 5,15,25,35,45,55, * * * *. These used to parse and now they raise an error, but we can clean these particular issue up in the dataset prior to upgrading so it's less challenging to handle.

Postel law:

be conservative in what you do, be liberal in what you accept from others

Accept trailing commas and 1,,2 extra commas.