Link against libmlton-gdb.a when compiling with '-debug true' or '-debug-runtime true'.
Update MLYacc library to pass both left and right position of token to error function.

Thanks to René Neumann for the bug report.
Merge pull request #27 from MatthewFluet/link-libmlton-gdb

Link against libmlton-gdb.a when compiling with '-debug true' or '-debug-runtime true'.
Merge pull request #28 from MatthewFluet/mlyacc-lib-error-fn

Update MLYacc library to pass both left and right position of token to error function.