add/mlpc

[karpathy]

still really bad.

• use const properly
• use int <-> size_t properly
• the naming conventions for our "kernels" are totally messed up and inconsitent. e.g. variables a,b,c should have grads da, db, dc in the correct naming convention.
• use model->inputs/targets properly, the way they are toggled atm is not good. the dataloader should be an independent, self-contained module and shouldn't "reach into" the model
• in general, all classes should be closed/indepedent and re-usable, and we shouldn't be reaching into their attributes and toggling them around from the outside.
• add omp