This patch adds a “doas” command alias to eshell for users who prefer
doas, similar to the existing “su” and “sudo” command aliases.

I'm unsare whether to use “TRAMP” or “Tramp” spelling. The existing
routines in the file use the former, but I've been informed the latter
is correct. A future patch should make all spellings (at least within
this module) consistent.

Additionaly, I've added a function for calculating the remote-path for
files accessed with doas. This function is currently limited to *only*
doas, because I didn't want to mess with the other su and sudo
functions, but there's no reason it can't be shared, and a future patch
should implement that sharing if this patch is considered desirable.

-bjc