wordmove should ignore or warn about trailing slashes in 'vhost'

[castilma]

$Title, to prevent others from the error in #641.

[alessandro-fazzi]

I've updated the doc as a quick way to warn users: https://github.com/welaika/wordmove/wiki/movefile.yml-configurations-explained#vhost

I'll also promote this to a feature request following this simple idea as mandate, thus enabling wordmove doctor to warn about the -almost sure- misconfiguration.

Thanks for prompting.

I'll proceed as soon as time will be mercyful ;)

[alessandro-fazzi]

Promoted to feature in #650 .