Use keyword arguments in response and simulate

[albop]

Some positional arguments in response and simulate functions are very error-prone:

• N and T
• m0, s0, e0, e1 can be easily mistaken one for another since they have the same type.

We should have methods with all of these as keywords, and possibly remove positional versions alltogether.

[gabriellequeran]

I can have a look at this.