VSIPL16 — Meaning of vsip_symmetry enum values inconsistent

The vsip_symmetry enumerator is used in a number of places, and in
general the VSIP_SYM_EVEN_LEN_* values are defined as "(Even) Symmetric,

length".

However, in the text there are sporadic mentions that imply that
symmetric here really means conjugate-symmetric; for instance, see the
bottom of page 567 ("The filter kernel can be even (conjugate) symmetric
or non-symmetric.") and the definition of the "kernel" argument to
vsip_*fir_create on page 612. This needs to be much more clearly and
consistently stated.

Regardless of whether the kernel is defined as symmetric or
conjugate-symmetric, the method for constructing the complete kernel
from the input in the symmetric cases is not defined. Is the input the
first half of the kernel, or the second half? Is the first half
conjugated, or the second half? This needs to be clearly specified.