Very small regex pattern tweak to allow Still to process column names that contain spaces

[nrminor]

Hi Daniel,

I've been working with Still to validate normalization in a very large tabular database that has spaces in the column names. After working through a panic traceback, it seems like the problem stems solely from the regex pattern in line 82 of schema.go, which matches for any symbol except for ":" to split out the column name from the rule. After altering the pattern so that it splits by ": ", it appears to be working as expected in my tests. Since it's working for me, I figured I'd submit a PR!

Let me know if you have any other questions, and thanks very much for the tool! It has been a huge help to me and the lab I work in.

--Nick

[danielecook]

Cool! This looks good, but it looks like my github actions is broken. I'll try to get around to fixing that later. For now you may need to rebuild until I get that addressed.

[nrminor]

No problem! I'm already working with a local build of my fork. Fingers crossed you don't find anything this breaks that I missed. I'm suspicious that this (apparent) fix was so simple!