Removals:
- Hermite, Fourier, and Sinc presented spurious numerical
  oscillations, making them unusable.  They are removed
  from this release.  Those may be added later if a
  satisfactory implementation can be made.

Improvements:
- Add a warning in Lagrange and Laguerre that these
  implementation are not robust against large stretching
  of the nodes.
- Rename GeneralPoly to Lagrange
- Improve testing of the poly_diff module