Incorporating various suggestions from LNT

gallery
  - wording changes
  - added 'stegosaurus' function
  - further documentation

gallerytrig
  - added 'AMsignal' and 'FMsignal'
  - further documentation

gallery2
  - added 'airyreal' and 'airycomplex'
  - rewrote description for 'bump'
  - further documentation