Avoid colons in filenames

[suddjian]

Fixes #217

I haven't tested this, I'm on windows right now and don't have make. But it seems pretty straightforward.

[raisjn]

thanks for doing this! looks good, but worth testing before merge

[suddjian]

Agreed on testing for sure, if someone with a dev env already set up would be kind enough to help there I'd be very grateful.

[raisjn]

harmony.tar.gz

PFA the built file (had to upload as .tar.gz)

[suddjian]

Tyvm for the build! What's PFA?

[raisjn]

PFA = please find attached. sorry about the corp speak

[suddjian]

Thanks! I'm going to be afk for a few days, I'll see about testing that when I get back.

[suddjian]

Finally got back to this! There were actually a couple more functions using get_date that I didn't find before. It looks like get_date is only used for generating file names, so I decided to change the way it formats the date instead of adding an extra sanitization step. (though this is my first time working with cpython, so maybe double check that)

I've tested this last commit, all functionality appears to be working correctly.