Squashed commit of branch findexe.
* bump version to 0.22
* Much improved support for finding and using helper programs
  automatically.
* error/warn improvements.
* documentation improvements.
* Load File::Which only if it is available. For helpe programs.
* Many pod formatting fixes.
* include version in user doc somehow. Can't find
  mention of any convention for including version number,
  or actually any example of including a version number.
  Need to find a better way.
* fix some bugs with viewing. Bugs remain, esp with gv!
* change command `viewer' to `startviewer'
  it conflicted with variable `viewer'
* remove pod2htmd.tmp