Gsl optimizer solver types

Adds all the available GSL multidimensional optimization solver types. I know that perhaps the *2 algorithms may be redundant, but GSL kept them older ones around, so I feel like we should as well (at least, in the absence of going in and looking at all the details).

Untested so far. Need to create unit tests to hit all these things.

@dmcdougall please make sure I didn't muck up the rebase.
Did you mean to use `m_step_size` instead of these hard-coded values?  You used them for the `*_fminimizer` below, but not here.