Revert example MOD files in user guide to mode_compute=4

The estimation examples in the user guide are not behaving nice with mode_compute=4, because of the non-deterministic nature of estimation. Many users were confused because on some runs, the example were failing because the hessian at the mode was not definite positive.

As a quick fix, the mode_compute option was changed to 6 in 4ec5016e and 7b59c012.

The problem is that the examples are now a lot slower than before.

We should revert back to mode_compute=4 when #85 (closed) is fixed and we have a way to fix the seed.