Log Message:

Update to 0.21.0

  Support for clang compiler was implemented.

  Documentation and presentation were updated. There are new projects
  using mk-configure.

  mkc_install is always used for installing mk-configure.
  This simplifies an installation process on non-BSD platforms.

  WARNS variable: support for icc was added.

  New variable LEXLIB library responsible for -ll/-lfl was introduced.
  See examples/hello_calc2.

  mkc_check_compiler: in order to differentiate icc from gcc, the
  check for Intel C/C++ compiler is run first.

  New target "filelist" that outputs a list of files for the whole
  project was introduced.

  Makefile: mk-configure's mk files are unconditionally installed to
  its own directory in order to avoid potential conflicts with
  system-wide sys.mk on BSD platforms.

  mkc.configure.mk: HAVE_FUNCLIB.main is always set to  1.
  mkc_check_funclibs is not run for checking presense of function
  "main" in libc.

  New variable MKCHECKS was introduced.

  Useless rule ".sh:" was removed.