Note that similar to __MKIT_PROJ_VERSION__, this value cannot be
reliably determined when outside git (e.g. distributor's build dir),
therefore must be kept inside dist source package.

Unlike version, though, user (ie. app developer, ie. mkit.ini
maintainer) most probably does not want to edit it, therefore we're
normally keeping it out of sight.

The value itself is normally just the last git commit's hash (SHA1 these
days), suffixed with ".dirty" mark if there were uncommitted changes
during build.  (Just the same as we do with semver())

If we're outside git and the hash could not be determined, that either
means the source package was mangled with or was built with older
version of mkit.  In either case, the value provided will be 'UNKNOWN'.

Some parts got a bit confusing over time, also there was repetition.

In this commit:

 *  the release fact gathering routines have been moved to separate
    module,

 *  some less useful routines have been removed,

 *  some internal interfaces have been changed to allow for more
    readable code.

Overview of changes:

 *  Fixed joining of DESTDIR and group root
 *  Added __MKIT_PROJ_NAME__ token for project name

Fix up the path joining logic:

 *  For obvious reasons, we panic if group's root is empty.

 *  DESTDIR can be empty, that's normal for installs such as when MKit
    installs its own dogfood.

 *  Root (which sometimes starts with PREFIX) may or may not start with
    slash; relative root such as that is also OK for installs like MKit
    or TFKit.

 *  Furthermore, DESTDIR may or may not end with slash; we have to address
    that and avoid joining the names.

Overview of changes:

 *  Added sanity checks for debstuff target
 *  Added new tokens: __MKIT_PROJ_PKGNAME__ and __MKIT_SELF_VERSION__
 *  Minor code and meta-data cleanups

MKit current version; this can be added in templates to aid maintenance
and debugging issues related to MKit.

The package name as used in distributions.

Overview of changes:

 *  Added debstuff target to help Debian maintainers
 *  `make clean` removes directories as well
 *  Rewrote route with sane(r) approach ro targets

But apply at least minimal safeguards from running `rm -rf /` or
similar catastrophic cases.

Simplify maintenance by moving list of valid_targets to a separate
function.  Both router and usage message are now consumers thereof.

This also changes format of the usage message.

Overview of changes:

 *  Move all project meta-data to mkit.ini (obsolete config.mk)
 *  Add tagline to common peoject meta-data
 *  Use more qualified tokens for replacement
 *  Improve mini-changelog

Make it clear what's related to the packaged project.

 *  Fix tag format errors
 *  Fix VERSION parsing from config.mk
 *  Fix sed error when generating changelog data

v0.0.0 vs vv0.0.0 vs 0.0.0

In local install, the files could be present, so relying on find to find
nothing did not work.  chmod must be properly sandboxed.

Hopefully this is now according to GNU standards.