Add vanilla bastion PKGBUILD
Add rxvt to makedepends, among other changes

Add rxvt to makedepends because bastion (and other programs that use nixstaller)
depend upon one of the following:

* xterm
* rxvt
* dtterm
* eterm
* Eterm
* kvt
* konsole
* aterm

See `GUESS_XTERMS` variable in file for details.

Display more useful message to user. Inform user that they can place binary in
$SRCDEST instead of downloading file from HIB servers, and rewrite messages to
be more proper english.

Reformat file. Replace tabs with spaces, and move `md5sums` further up in file
to shut up namcap warning. Other changes to presentation of code.
Add periods to end of sentences