build-dep: support templates, srcpkgs, archives
A comprehensive refactor of build-dep and related pkgstyle functionality to install or list (-l/--list) build deps from templates as well as from source packages.
The new default approach of parsing build deps from templates has following advantages:
- works directly on project source without archive/srcpkg build
- requires less tools to work
- is faster
Alternatively, -s/--srcpkg makes apkg parse build deps from source package which is slower but more robust in some cases.
Build deps can also be extracted from archive containing proper distro/ files with -a/--archive option in both template and --srcpkg mode.
-u/--upstream option uses upstream archive (get-archive) to get build deps from for maximum convenience.
Fixes: #34 (closed)