VSIPLXX13 — Incorporate the VSIPL++ DDA API into the VSIPL Specification

Direct Data Access (DDA) provides the means to access block data via raw pointers, independent of how the block holds the data, and regardless of whether or not the block is bound to user-specified data or VSIPL data. This functionality provides for a more extensible math library by enabling the use of external library calls on user-specified blocks without releasing them, and on VSIPL blocks in general. This API is already incorporated into the VSIPL++ specification and should be incorporated into the VSIPL specification as well in order to bring the two specifications closer together.

Please note that this issue is similarly being tracked on the specification repository: https://github.com/vsip/specs/issues/8

Added a new DDA API to VSIPL (VSIPL, sections 2.5, 4)