z3: move to multiple output packages

The Z3 source code is effectively compiled into two completely separate
objects: the z3 binary file, and the libz3.so library -- but the binary is not
linked against the shared library, it simply incorporates all of the object
files. The Z3 code base results in an ~25MB object on x86_64-linux. As a
result, splitting bin/ and lib/ results in a 50% reduction in closure size.

(The include/ directory is also surprisingly large at .5MB...)

This also splits the python API into a completely separate .python attribute,
as well.

Signed-off-by: Austin Seipp <aseipp@pobox.com>