fminsearch update1

For some reason, costFunction.m did not upload in the previous commit
(only the auto-save file costFunction.asv uploaded), so here it is.

Also, I added some comments to simulODE.m, as well as changed it such
that the differential equations for the data sets (involving S and X)
are uncommented, while the differential equations for the test data set
(involving x0 and x1) are commented out.

Final comment: when running fminsearch, import fminsearchData.mat, NOT
Tumor Data (column).mat.

Other than these above changes, the description from the "fminsearch
working!" commit still largely apply.