Version -> 0.29.0
Makefile: gmake version
Makefile.inc: gmake version
main.mk: gmake version
add mk/mkc.gmake.mk library
mk/mkc.mk: gmake version
mk/mkc.lib.mk: gmake version
mk/mkc_imp.preinit.mk: gmake version
mk/mkc_imp.mk: gmake version
mk/mkc_imp.lua.mk: gmake version
mkc.gmake.mk: additions

Add CLEAN_TARGETS constant for common use
Added functions
 - not
 - is_defined
 - sed
 - filter-glob
mk/mkc_imp.pkg-config.mk: gmake version
mk/mkc_imp.conf-cleanup.mk: gmake version
mk/mkc_imp.conf-final.mk: gmake version
filter-glob function: change argument order, like filter
mk/mkc.gmake.mk: add toupper
mk/mkc_imp.conf.mk: part of gmake version
mk/mkc_imp.conf.mk: gmake version part2