Captions and attributes for images and tables during export

Captions and attributes for images and tables during export

Tables, and Hyperlinks that represent inlined images, can now be
equipped with additional information that will be used during
export.  The information will be taken from the following special
lines in the buffer and apply to the first following table or
link.

  - #+CAPTION: :: The caption of the image or table.  This string
       should be processed according to the export backend, but
       this is not yet done.
  - #+LABEL: :: A label to identify the figure/table for cross
       references.  For HTML export, this string will become the
       ID for the `<div class="figure">' element that encapsulates
       the image tag and the caption.  For LaTeX export, this
       string will be used as the argument of a `\label{...}'
       macro.  These lables will be available for internal links
       like `[[label][Table] ]'.
  - #+ATTR_HTML: :: Attributes for HTML export of image, to be
       added as attributes into the `<img...>' tag.  This string
       will not be processed, so it should have immediately the
       right format.
  - #+ATTR_LaTeX: :: Attributes for LaTeX export of images, to
       be inserted into the optional argument of the
       `\includegraphics[...]{file}' command, to specify scaling,
       clipping and other options.  This string will not be
       processed, so it should have immediately the right
       format, like `width=5cm,angle=90'

For LaTeX export, if either a caption or a label is given, the
element will be exported as a float, i.e. wrapped into a figure
or table environment.