Parsing support for multiple keysyms per entry

Parsing support for multiple keysyms per entry

Instead of allowing only one keysym per level per group, do as the
external API indicates and allow multiples.  The existing syntax is:
    key <AD01> { [ q, Q ] };
where the new syntax is:
    key <AD01> { [ q, Q, { H, E, L, L, O },
                 { Y, E, S, space, T, H, I, S, space, I, S, space, D, O, G } };

to make the key in the extreme top left of the keyboard do pretty
surprising things in levels 3 and 4.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>