hook functions: die_cannot_run()

+ qwhich(): use "hash" instead of "which"
hooks: use die_cannot_run()
console interpreter: do not fail if var is not set
overlay/creator: fix comment
config/entryutil: iter_entries_with_value_type()
config/fielddef: log path of the missing licenses file
config entry map: make LICENSES_FILE configurable
let's run on debian #1: roverlay-setup

This commit adds basic support for target-specific setup
via the "--target-type <type>" switch.

So far this affects config file creation only and there are 2 choices:

* "gentoo": have portage and a PORTDIR
* "foreign" a.k.a. "not gentoo": neither portage nor PORTDIR available
Makefile, generate-config: + R-overlay.conf.others
roverlay/argparser: fix

Pass **kwargs when creating the parser object.
setupscript, arg parser: add ROVERLAY_TARGET_TYPE

... to epilog
Makefile: parallel generate-config
Makefile: $ROVERLAY_TARGET_TYPE

ROVERLAY_TARGET_TYPE controls which files get installed:

when gentoo:
=> config/R-overlay.conf.install
=> no licenses file

when others:
=> config/R-overlay.conf.install.others
=> install files/licenses to $DATADIR/licenses

Also added a "generate-licenses" target for creating files/licenses.
update generated files
fileio: catch EOFError
roverlay-setup: load parser defaults file
update roverlay-setup bash completion
bin/scripts/genfiles: minor doc update
doc/html: update