vertical shifting of inline images

[Werner LEMBERG]

Right now, texinfo positions inline images on the baseline, with no
possibility to change this vertically.  I suggest that this gets
improved – here are some ideas as a request for comments.

* A new command

    @imagevertorigin ORIGIN

  ORIGIN specifies the origin of vertical offsets.  Possible values
  are 'baseline' or 'x-height'.  Example:

    @imagevertorigin x-height

* A new command

    @imagevertoffset OFFSET

  to vertically offset all following images relative to the origin set
  by `@imagevertorigin`.

  OFFSET is either an absolute value or relatively defined using the
  image's height with a factor, similarly to LaTeX's `\height` macro
  in `\raisebox`.  For example, centering all images vertically on the
  x height axis could be done with

    @imagevertorigin x-height
    @imagevertoffset -0.5@height

* Another optional argument to @image

    @image{FILENAME[, WIDTH[, HEIGHT[, ALTTEXT[, EXTENSION[, OFFSET]]]]]}

  to vertically offset an inline image relative to the vertical origin
  as set by `@imagevertorigin`.  OFFSET overrides the global vertical
  offset set by `@imagevertoffset`.


     Werner