Implement Tag SpecialKey

[krypt102]

Fixes #36
This PR might be dependent on #216 due to xtypeof being removed, if necessary we can wait for that to be merged and then modify this code accordingly.

[dphfox]

The issue was marked as 'needs design'. Please be wary of implementing features before a design is finalised.

In particular, we have not yet decided between [Tags] and [Tag "xxx"] styles. This PR is blocked until a style is decided upon - right now, it looks like we might be inclined to choose the latter over the former. Since this PR implements the former, it's likely you're going to have to redo your work, which is why we don't want pull requests for things that haven't been finalised - your time is as precious as ours, and we don't want to waste it.

[krypt102]

The issue was marked as 'needs design'. Please be wary of implementing features before a design is finalised.

That's my bad once again, the second time I've done this (idiot me), will be more aware of it next time I go to read.

I'll close this for now, and once we decide and it becomes approved I'll reopen!

[dphfox]

The issue was marked as 'needs design'. Please be wary of implementing features before a design is finalised.

That's my bad once again, the second time I've done this (idiot me), will be more aware of it next time I go to read.

I'll close this for now, and once we decide and it becomes approved I'll reopen!

Don't be too hard on yourself! It's okay to not know, as long as you keep it in mind for the future :)

[dphfox]

Issue is now approved, feel free to reopen

[krypt102]

Reopened here