Rethink Checkscalasig

[xeno-by]

Checkmjar (currently called "Checkscalasig") has really unlucky history.

One of the pull requests in August inadvertently broke Checkmjar in a really outrageous way: it started producing false negatives, ignoring tons of legitimate errors. By the time when I found that out (#192), fixing the brokenness was no longer easy - although the fix for Checkmjar was trivial, applying it broke MjarTests in a very non-obvious way.

Since I was preoccupied with something else at that point, I decided to push back fixing Checkmjar, and of course, more and more issues started creeping in: #211 and #228. The technical debt around Checkmjar was becoming more and more unsettling.

Surprisingly, despite that we were effectively lacking any systematic way to check mjars, that didn't stop us from making progress. It turned out that despite the tons of errors that Checkmjar used to show us, we only needed to fix a handful of issues to successfully compile a pretty big case study project. While this anecdote doesn't prove anything, it definitely gives some food for thought.

In #241, I decided to take a radical step forward. I announced Checkmjar bankruptcy and deleted Checkmjar and everything that relied on it (Diffmjar and MjarTests). Let's start from scratch and get it right this time.