Loosen signature for some matmul functions as a prepartion for array views.

The main thing here is to use BLAS when calling dot on view of vectors.
You could argue for both. This method only wraps a scalar result from a dot operation in a vector and I think that make sense for any `AbstractVector`, but you are right that `BLAS.dotu` only is defined for `StridedVector{T<:BlasFloat}`s. However, my definition will actually give a no method error for `AbstractVector{T<:BlasComplex}`s instead of transposing `x` explicitly so I'll change that signature.