VSIPL16 — VSIPL and VSIPL++ should define version macros

The VSIPL++ (and VSIPL) standards should define version macros, so that application code can be conditionalized on what version of the library they are being compiled with.

This should be done with numeric macros (i.e., VSIP_VERSION=1 and VSIP_VERSION_MINOR=2) to enable numeric comparisons.

In addition, there should be separate macros for VSIPL and VSIPL+, and either there should be separate version macros for VSIPL+ and Parallel VSIPL+, or there should be a macro ("VSIP_PARALLEL"?) to indicate whether the Parallel VSIPL+ pieces are supported.