rewrite explicit Kripke structures and their parser

Fixes #4 and fixes #5.

* NEWS: Mention the change.
* src/kripkeparse/: Delete.
* README, src/Makefile.am, configure.ac: Adjust.
* src/kripke/kripkeexplicit.cc, src/kripke/kripkeexplicit.hh,
src/kripke/kripkeprint.cc, src/kripke/kripkeprint.hh: Delete.
* src/kripke/kripkegraph.hh: New file.
* src/kripke/Makefile.am: Adjust.
* src/parseaut/parseaut.yy, src/parseaut/public.hh: Add
an option to read kripke structures.
* src/tests/bad_parsing.test: Delete.
* src/tests/Makefile.am: Adjust.
* src/tests/kripke.test, src/tests/parse_print_test.cc: Rewrite.
* src/tests/ikwiad.cc, src/tests/parseaut.test,
iface/ltsmin/modelcheck.cc, wrap/python/spot_impl.i: Adjust.

configure.ac

@@ -206,7 +206,6 @@ AC_CONFIG_FILES([
   src/bin/man/Makefile
   src/graph/Makefile
   src/kripke/Makefile
-  src/kripkeparse/Makefile
   src/Makefile
   src/misc/Makefile
   src/parseaut/Makefile