Log Message:
Update to 0.23.0
  mkc.subprj.mk:
    - Support for "virtual" subproject was added. Subprojects listed
      in SUBPRJ and SUBPRJS_DFLT are not necessarily associated with
      a subdirectory. See examples/hello_superfs for example.
      Virtual subproject is a way to group several subprojects into
      new one.

  New variables were introduced: COPTS_<proj> OBJCOPTS_<proj>
  LDADD_<proj> LDFLAGS_<proj> CPPFLAGS_<proj> \ 
CXXFLAGS_<proj>.
  See the manual page for details.

  Fix: OBJDIR_<subdir> variables now always contain full paths.

  Fix in mkc_which(1). Now it differs directories and regular files.

  Minor fixes in regression tests for EXPORT_SYMBOLS.

  mkc.lib.mk:
    - SHLIB_MINOR unconditionally defaults to 0

  More slides in .pdf presentation:
    - cross-compilation
    - EXPORT_SYMBOLS

  Fixes for Pascal support

  Minor fixes in the man page