Replace %Y with %y in deadlines to fix the generated iCal

[Enrico204]

This pull request replaces %Y with %y in deadlines to fix the generated iCal, so that it can be imported in Google Calendar and other tools. Fixes #162 and supersedes #231

Future pull requests should pay attention to not have %Y (uppercasee Y) in the deadline, as only %y is allowed

[Enrico204]

To be honest, @clementfung I think that we should fix the template itself to allow %Y, so that there will be no problem even if you merge deadlines with uppercase Y. Appending replace: '%Y', tyear after replace: '%y', tyear in all iCal templates should do the trick. However, I have no experience with those templates, and I have no way to test them (I think). Do you have some experience with those? Or, do you have a way to test that and revert the change if there is a problem?

(if we want to proceed and fix the template, we can close this pull request and open a new one)

[clementfung]

@Enrico204 Thank you for looking into this and sorry for the slow response!

To support rolling deadlines, we currently use '%Y' to designate the previous year, and '%y' to designate the current year: https://github.com/sec-deadlines/sec-deadlines.github.io/blob/master/static/js/main.js#L24

So accepting this change would be a breaking change for those deadlines. I also don't have much experience with generating and testing iCal, and I could take some time to look into that further (no promises on when that would be...).

So I think the options are:

1. Remove support for '%Y' and find a better way to handle the years of rolling deadlines in the js file
2. Remove support for rolling deadlines, and explicitly write the year for these deadlines moving forward.
3. Find a way to fix the iCal template, as you suggested.

Option 2 is honestly not that bad, since we already have to update the "year" field every year anyways.
Any thoughts from you or others?

[Enrico204]

Oh, I missed the difference between %Y and %y! Indeed, this PR cannot be merged.

I would suggest to fix the iCal template (option 3). The placeholder might be useful in some cases (like the one modified in this PR), and it doesn't seem to complex to support.

I suspect that defining a new variable and a new replacement should suffice. Something like {% assign tprevyear = 'now' | date: '%Y' | minus: 1 %} somewhere in the file (like in the same line as BEGIN:VCALENDAR), and then add replace: '%Y', tprevyear after replace: '%y', tyear. It will define a new variable using the current year and decrementing it by one, and then it will replace %Y with that year.

But I am quite busy right now, I can't try it :-(
Probably I can setup a test env after July 10th

[Enrico204]

Closed as fixed by #324