Allow usage_is caller specify exit status or suppress exit completely

Since functions cannot start with '-' (and funky names are discouraged
anyway), it only adds more complexity to the arg router.

grep at the end of main pipe ensures not only correct exit status
but also throws away empty lines--but should not do it in strict
mode.

I.e. ffdoc works now.

Major rewrite of listing code.  New version is more readable, more
usable (no need for lsfun() in ffoom now)  and suports wildcards.

Fastfoo libraries are not intended for interactive sessions (use *fff*),
we are only enabling this to aid development and testing process.

Contains charmenu, a utility function to help define and utilize
interactive "character menu" as we know it from yum, apt, git and
many, many other CLI tools.

Since these files do not contain build-time anymore, they don't need to be processed by mk.sh as such, hence can have their final form

... so that we don't have to care if other modules have already created
it (as long as our path inside it is unique)

All this module does is create a temp directory FFOO_TMP, that can be
shared among modules.  This simplifies clenanup but should be only
used very rarely and only by modules (i.e. not by user code).

 *  Support `date`'s +FORMAT notation.
 *  Use FFOO_TESTING_ARTIFACTS if argument not provided

Debug calls with command line to be executed are dangerously easy
to become obsolete and misinforming.  They should be only used ad-
hoc for a very short time (i.e. when debiugging the command), or
replaced by construct such as

    cmd="some command --with args | maybe pipe"
    debug -v cmd
    $cmd

provided it's safe.