blas64: add row/col major conversion methods

Created by: kortschak

Reference #138.

This covers the types that are supported in mat and makes no change to the API other than adding the conversion tools. My sense of symmetry says that the row major types should be labelled as such, but I could get over on the basis that we are natively row major and the column major types are for external use.

asm-dependent code can come later as can generation of float32 and complex equivalents.