Fix for bias, cross-fold option, unseen feature support.

Hey Kevin,

Any interest in these changes? The unseen feature support reserves 1 for unseen features. During prediction, any new features get assigned this id. The cross-fold is fine, though I haven't added any code to compute accuracy values as my own code is only for two classes (e.g. not sufficiently general).

The bias support was missing the adjustment to n when the bias is active. You might also want to consider changing the default for the bias to 1 even though it differs from liblinear's defaults. It is apparently rare to need no bias in practice and disabling it might harm accuracy.