Remove prefix diff highlighting

This was well-intentioned but ended up being more confusing than it was worth.
It's always confused me when one digit gets un-highlighted in one of these
displays. The straw that broke the camel's back was when I got a "#1 -> #16"
change where the numeral "1" was un-highlighted. To fix this right would be
way more trouble than it's worth; I'm glad to be rid of this detail.

Conflicts:
	docs/changelog.rst
Malformed date queries no longer crash