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LUA_INCLUDE belongs to CPPFLAGS, not CFLAGS
Add /usr/local/include and /usr/local/lib to CPPFLAGS and LDFLAGS

This allows to avoid extra options for BSDs and strangle Linux systems, where
some libraries may be installed under "/usr/local" prefix.
Clean up and merge Linux and BSD instructions

 * Now BSDs don't require setting environment for configure.
 * No default Makefile any more.