VSIPL16 — Conv. 'kernel_size()' incorrect for symmetric kernels

Copied from an internal bug report:

PROBLEM: Convolution accessor 'kernel_size()' is defined to return the
domain having the same length for each dimension as 'filter_coeffs'.
However, when constructing a convolution with a symmetric kernel
(sym_even_len_odd or sym_even_len_even), 'filter_coeffs' only holds
a subset of coefficients. In those cases, the true kernel size is
larder (For example, in 1D convolutions the true size will either '2 *
filter_coeffs.size()' or '2 * filter_coeff.size() + 1').

In contrast, the C-VSIPL spec defines the kernel size as M, and
specifies the size of 'filter_coeffs' as either M if symmetry =
non_sym, or 'floor(M/2)' if 'symmetry == sym_even_len_

'.
Queries to return the kernel size of a convolution return M.

PROPOSED FIX: Change wording of 'kernel_size()' accessor (and
Convolution constructor effects) to indicate correct kernel size.

TODO: Review specification of Correlation, FIR, and IIR for similar
error.