Some unique deaths should not be unique

[cheryl]

This was raised in irc, I don't remember by whom. The example was that "killed by a couatl" should be indistinct from "killed by a couatl of $DEITY". There are probably other examples.

[cheryl]

Could be a duplicate of issue #21

[mathematicalcoffee]

FYI #48 pull request implements some of the widely-agreed-upon death normalisations. #43, #33, #21 seem to all be related to this.