Deprecate support for macOS Sierra (10.12) and before

[uranusjr]

I did some counting on OS versions of recent updates (yes, I collect device information when you update MacDown). This is the result from the last 1000 downloads:

Major Version	Count
10.12	375
10.11	514
10.10	75
10.9	36
10.8	0

So either nobody installs MacDown on 10.8 machines, or (remembering this is only statistics for updates, on installations) people running 10.8 don’t update. So this might be a good reason to discontinue 10.8 support. This will probably happen in 0.7, but I don’t have a timeline for that release.

[FranklinYu]

This report about market share may also help decision.

[FranklinYu]

As we all know, Apple only supports last three macOS: the current one, and two previous ones. I plan to deprecate support for older macOS because it’s difficult to test.

Currently this means Sierra (10.12) and before will be supported with best effort. Not actively looking for fix of bugs; Pull Requests for such fix will be discussed case-by-case.

[iJaack]

@uranusjr do you have updates on this? I would like to contribute to the development, but first I would like to understand which are the priority issues to tackle :)

[gdunge]

I am on High Sierra 10.13.6, so as far as I'm concerned you can go for it :)

[FranklinYu]

@iJaack Current priority is to resolve #1104 (which I still have no idea how to solve). If you want more then the label “help wanted” (with updates within last two years) could be a good start.

(I have plan to clean up stale issues and apply stale bots there after.)