The libslvs library and CDemo program can now be built by Autotools. A few
code changes were needed for this: C++ comments in C code had to be
converted, constraint.cpp required some massaging, and fltkutil.cpp needed
a stub for InitHeaps().
The SolveSpace top-level directory was getting a bit cluttered, so
following the example of numerous other free-software projects, we move the
main application source into a subdirectory and adjust the build systems
accordingly.
Also, got rid of the obj/ directory in favor of creating it on the fly in
Makefile.msvc.
