== New: _#pragma search ..._

I got tired of the relative links in my blog drafts (written in an
entirely different directory than their eventual home) not working.
So, introducing _#pragma search_; this adds additional directories to
search for pages when resolving relative links, both WikiWords and
explicit ![[...]] links. The directories listed in a search pragma must
be absolute path names, and are searched only after the hard-coded
possibilities have been exhausted (including the alias directory for
WikiWords).

You can't have both a _#pragma search ..._ and a _#pragma pre_
in the same page, partly because it doesn't make any sense.
(This is the simple way of getting out of handling multiple
_#pragma_ directives.)