added small warning in automatically generated opt_* files

add option to specify the size of the small axes

- new "Delete Empty Views" command
- new View.MinX, View.MinY, View.MinZ, View.MaxX, View.MaxY, View.MaxZ options
- added example on how to do simple volume visualization

- Moved all the Raise[][] stuff out of the drawing routines, and into
  Graphics/Post.cpp

- New 'generalized raise' mode (can use arbitrary expressions, possibly
  with external data sources, to raise/offset views dynamically). Original
  patch by Nicolas Tardieu. Merci Nico!

new solver options: SocketCommand and NameCommand (patch by
<C.Stott@surrey.ac.uk>)

bring option docos up-to-date

Set View.ShowTime=2 to show the time value even if the view contains a single
time step..

typos

update for gl2ps

update option doc

Add DisplacementFactor option + rename ArrowScale->ArrowSize and
ArrowType->VectorType

Small corrections

Corrections apres relecture / part 1

More work on chapters 1 and 2. Should be mostly OK now.

Major rewrite of the Overview section + web page

small updates

... in @node confuses makeinfo

Added "gmsh -doc" to automatically generate the texinfo documentaion
for all the options.