blas/netlib: use panic string consts instead of string literals

Created by: vladimir-ch

This got bigger than expected. I looked at the code generation to see how and where to change the panic strings and I noticed a few things that could be polished and one thing led to another and this is the result.

There are now fewer parameter check functions and some of them got much bigger but I think that it is easier to see now how the code is generated. The bool that was previously returned made this not so easy.

Most of the changes in the output blas.go should be just text movement with some refinement here and there. It is best reviewed commit by commit.

Please take a look.