VSIPL16 — Fir<> has duplicate 'symmetry' accessor, member

The Fir<> class is required to include both "static symmetry_type const
symmetry" and "symmetry_type symmetry()". This duplication of names is
illegal, and the duplication of functionality is pointless. (Thus, the
Mentor Graphics implementation provides only the const member, not the
method.)

Less illegally, the continuous_filter member and continuous_filtering()
method duplicate each other. Similarly, in [signal.convol] we have a
misspelled symmtry member and a symmetry() method, and in both
[signal.convol] and [signal.correl] we have a supprt member and
support() method. These duplicates and misspellings are confusing and
redundant, and should be removed.