Optimizer specification

[andrew_peterson]

There are a couple of issues with the way optimizers are specified in Regressor.init:

1. The user can specify any optimizer function they like (this was the original behavior before the string shortcuts were added). This should be noted in the docstring.

2. The user can specify optimizer kwargs, such as maxiter. In principle, this should also work if the user specifies a string shortcut for the optimizer. If the user does so, these are arguments are ignored. It should be setup that they add to a dictionary.

[andrew_peterson]

Correct optimizer specification in Regressor.

Resolves issue #100.

→ <<cset 012b87fd700a>>