Use MKIT_INI to specify path or default to mkit.ini in $PWD

 *  Move targets to mkit/mkit.mk,
 *  make `mkit/make` and rest of mkit use MKIT_DIR for own path.

The version based on config.mk has been finalized to include more
features:

 *  Build variables are now defined in config.ini.
 *  The ini system can self-reference other keys (up to several levels).
 *  Some config (namely `ENV` section) can be overrided by environment
    variables.
 *  The installer is now more portable (ported to saturnin so far):
    everything can be defined in config.ini

Make it

 *  more flexible,
 *  more readable,
 *  faster,
 *  take care of manpages (not fully done yet),
 *  take care of dist list,
 *  little bit more polished in various other things.

A more conventional hierarchy

 *  Instead of cp, use *install*.
 *  Store paths in paths.ini.
 *  Allow arbitrary number of path groups (bin, man, share, libexec...).