anonymize

A version of anonymize that allows passing in a custom minimum length

When printing strings to logs sometimes we want to print useful debugging information about users or positions. But we don't want to leak things like usernames or locations. So this function if given a string, will return a string which is a maximum of three characters long, taken from the tail of the string. Which should effectively hide real usernames and locations, but still let us see if values were zero, empty or different.