Created basic CMake files.

Created basic CMake files.

xuni can now be built with autotools or with CMake. CMake is much
faster, though at the moment it only supports libexpat and has no dist
target. (Which is pretty much the same as the autotools system.)

CMake also has other advantages: for example, it doesn't create
libwidget.a and so on.

Note that src/test/test.so was renamed to src/test/libtest.so due to the
way that CMake creates shared objects. (Perhaps autotools would be able
to automatically create this file now.)