Lenstool

Currently the syntax of the parameters in the potfile is very different between core radius and cut radius:

- lenstool expects a single value after the keyword core (or corekpc) : like "corekpc 150" and fixes the core to this value.

- lenstool expects 3 values after the keyword cut (or cutkpc): like "cutkpc 1 100 150" to optimise cutkpc between these two parameters.

The main confusion is that "core 0 150" fixes the core radius to 0, while "cut 0 150" fixes the cut radius to 150, which could be a source of confusion.

Ideally we would like to homogenize the two parameters in a potfile, and allow at the same time for the optimisation of the core radius.