Many doc improvements for Circulation (#175)

- More precise doc for members.
- Several doc fixes.
- Add doc for public types.
- Better formulations.
- Add useful notes to the problem description.
- Use supply instead of excess in the doc.
- Hide the doc of the traits class parameter.
- Use \tparam for template parameters.

 /* Define to 1 if you have CPLEX. */

 #undef HAVE_CPLEX

 /* Define to 1 if you have GLPK. */

 #undef HAVE_GLPK