Remove all power-of-two requirements for function tables

[joachimheintz]

I think it is not any more true that function tables need to be power of two.
but still it is written in the manual, like for GEN27:

size -- number of points in the table. Must be a power of 2 or power-of-2 plus 1

can it be removed?

[tjingboem]

list of GENs where this is mentioned:
./gen01.xml
./gen02.xml
./gen03.xml
./gen04.xml
./gen05.xml
./gen06.xml
./gen07.xml
./gen08.xml
./gen09.xml
./gen10.xml
./gen11.xml
./gen12.xml
./gen13.xml
./gen14.xml
./gen15.xml
./gen16.xml
./gen17.xml
./gen18.xml
./gen19.xml
./gen20.xml
./gen23.xml
./gen25.xml
./gen27.xml
./gen30.xml
./gen31.xml
./gen33.xml
./gen34.xml
./gen43.xml
./gen49.xml
./gen53.xml
./genexp.xml
./genfarey.xml
./genpadsynth.xml
./gensone.xml
./gentanh.xml
./genwave.xml

[vlazzarini]

I think it can in this case (GEN27), but some (the FFT-based GENs) may need to be power-of-two because of the Radix-2 FFT used. We can change this in Csound 7 to use mix-radix FFTs.

One issue that arises when not using power-of-two sizes is the question of guard point type, which is defined indirectly via the table size (it may have been a great idea then, but it's a horrible one now). Basically, there is no way to specify an extended guardpoint for non-power-of-two sizes.
We will need to tackle that in Csound 7.