doc/archdep.txt was the reason to look closer,
and some other files needed a bit of facelift
by now too (would be better to do that in sync).

Thanks cas@ and Ivan Khakhaev for feedback!
My docs are clearly not the best in town,
please help bring those into shape :-)

This change is done to reduce ambiguity in some cases;
the previous intention has been to ease navigation when
staying in a particular directory, now it's been changed
in favour of convenient toplevel `git grep' in fact.

Both variants have their pros and cons, I just find myself
leaning to this one by now hence the commit.  Feel free to
provide constructive criticism :)

Some path-related bitrot has also been fixed while at that.

It was less clear/greppable what "installer" refers to...
or maybe so it seems to me.

These have been proofread somewhat to correspond
to the current state of affairs; a missing one
was added for fonts feature.

Minor tweaks to toplevel docs as well as some doc/*.txt,
doc/variables.txt renamed to doc/params.txt, and a brand new
doc/pkglists.txt is added (thanks manowar@ for his considerations).