fix(lua): make testudata compatible with Lua 5.1

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(lua/sexpr): make sexpr bindings robust

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(lua): add test driver for Lua binding tests

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(lua): invoke Lua binding tests from ctest

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(lua): use assertions

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(lua/numerics): errors when cross-compiling for Windows

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(travis): enforce windows build to use cmake-2.8.11.2
chore(cmake): switch the ordering between gmp and mpfr