Improvements on Tyre.rep

[Drup]

It could be possible to improves Tyre.rep by adding a ~min and ~max optional arguments, similar to Re.repn.

The case where max is provided could be optimized to avoid reparsing (by manual expansion of the repetition). We need to measure how re handles such manual expansion for large values of max.

One thing that is still unclear to me is what we should do for unparsing. Do we enforce the length constraint or do we just let the user provide whatever it likes ?