Tweak: Allow Hex SSPs to be even-dimensioned + Modify SSP Kernel names for consistency with behaviour

[jkbchouinard]

• Hex SSPs

  • Typically limited to 6RS+1 formation, which is a generic formulation for prime numbers
  • Allowing even representaitons makes them more compatible with other SSP and SPA methods, particularly neural representatations in Nengo SPA
  • Enabled through optional 'even' parameter

• Kernels

  • Previously introduced with names inconsistent with actual behaviours, this rectifies that error and characterizes each by their actual behaviour (jinc->hypergeom[etric], sinc->jinc)