Raw VHDL interface should be bits per stage not slices

[JulianKemmerer]

Currently for basic things like adders ex. 32 bits is divided by the slices specified
[0.5] = slice into two pieces = two 16b stages

First this is annoying because [0.499] is the same slicing (etc w/ close FP values) but still gets a different file, file name etc, blegh

Also its important to know how many bits per stage as being used. As in #46 and #48 and #45 we want to know what hardware is produced by the synthesis tool - some bits per stage implement better than others, etc.

[JulianKemmerer]

Thanks @suarezvictor prompting this into an issue