Post big-split tasks

[mohawk2]

The releasing of all the non-fundamental modules as independent CPAN modules (#119) has been completed. Still to do:

• making the PCHIP funcs be kernels, not separate C file
• fix the type-conversion gremlin revealed in FFTW3 work Type-selection of xform is wrong when has complex Pars, and converted [o] Pars in flowing xforms don't work #511
• rename diffover to numdiff - see also https://sourceforge.net/p/pdl/mailman/message/58844156/
• include a partial (with a degree param, subtractive Pascal's triangle convolution) - see https://sourceforge.net/p/pdl/mailman/message/58843767/
• making ndarray readonly so it errors if passed as output - see https://sourceforge.net/p/pdl/mailman/message/58849211/

After releasing 2.096:

• PDL::Slatec:
  • remove PCHIP stuff from (the EISPACK stuff in there, rs (symmetric), is different from (though unlikely to be much better than) the port of rg (general) in MatrixOps/eigen.c - I got confused by eigens.c, but that's from SSLib, not EISPACK)
  • say it's deprecated in favour of PDL::LinearAlgebra
• update with lib/*.pd stuff:
  • Proj4
  • GSL
  • Stats
  • P:LA (and finish removing pp_defc stuff)
• update TriD with code-yoink
• update FFTW3 to exploit fixed type_coerce