miniblog.

I'm increasingly doubtful that commit messages should be entirely immutable. I sometimes find myself editing or commenting on merged pull requests, to help future readers. Phabricator appended a URL to commit messages, which helped. In principle PR merging could do the same thing.

I'm adding a += operator to my programming language, because writing `x = x + 1` is tedious. This opens the tricky design question of which operators should support this. Is += and -= sufficient, or do you expect things like >>= and **= to be available?

Chekhov's repro: If a line of code is included in a bug report, it should contribute to the debugging somewhere.