Ensuring consistent transforms for KernelPCA
Taking @vene's changes into account, thanks!
Taking @jakevdp's comment into account
Added more verbose documentation to kernel_pca.py
Specifying that X_fit_ will not be None. @jakevdp
KernelPCA: Fixing more formatting of docstring
Addressed @vene's documentation comments
Addressing that dual_coef_ might not be present in model in docs. @vene