Old issues related to learning track

Of the 62 issues that were still open yesterday, many relate to previous planning of a learning syllabus. Some of those are clearly now obsolete (superseded by recent PRs), and have been closed.

That leaves about 20 which concern things still be be addressed on the new syllabus. Several exercises were drafted at the time, but are currently deprecated. Some of these may be reactivated in future, depending how the syllabus progresses.

I will close these issues for now, but want to document their existence in case they become interesting again.

- #601
- #600
- #598
- #597
- #587
- #586
- #585
- #584
- #583
- #581
- #580
- #579
- #573
- #572
- #571
- #351
- #302
- #306
- #307
- #309

_As a personal aside, I should note that this level of tidiness is quite out of character for someone who is the polar opposite of [Marie Kondo ](https://en.wikipedia.org/wiki/Marie_Kondo)_ 😲