GBMatrix constructors for transpose and adjoint matrices

[Gregstrq]

Since Transpose{T, SparseMatrixCSC{T}} and Adjoint{T, SparseMatrixCSC{T}} are used as place-ins for CSR matrices, it may be a good idea to add GBMatrix constructors for these types, which would directly construct GraphBLAS matrices in byrow format.

[rayegun]

Good idea, will do!

[rayegun]

@Gregstrq what do you think is the proper interpretation here? Should I take a A::Transpose{T, SparseMatrixCSC{T}} and essentially pass the fields of parent(A) directly to pack_csr?