Enable PDF document building

Images are still encapsulated postscript in the most part but pdflatex will
now be used and will automatically convert the EPS files to PDF. Many
pdflatex installations do not do the automatic conversion.

Components that explicitly override the default documentation macros will still
build postscript files. This includes Star2HTML, AST and ECHOMOP.

This work is associated with Issue #5
SC/5: Fix bounding box

Needed to adjust width in latex file to take this new bounding box
into account
SC/13: Convert GIF files to PNG

To be consistent with the conversions required for other documents
that use pdflatex.
SC/15: Switch to pdflatex

All the images seemed to be bitmaps so converted the GIFs to PNG
format so that pdflatex can use them natively without needing
the EPS files or converting them to PDF.

Two animated GIFs remain but the PDF document uses PNG versions of
those.
SG/8: Build with pdflatex

Deleted the colour example files and simply use them directly in
the document building phase as PNG images (so that pdflatex
can pick them up directly). Remove grey versions from document
completely. Converted remaining EPS files to PDF.
SUN/249: Rename image files to standard form with doc num prefix
SUN/249: Build with pdflatex

- Converted GIF images to PNG
- Converted EPS files to PDF
- Prioritised PDF over PNG (pdflatex picks up PNG over PDF by default)
pisa: SUN/109 now uses latex2e

- Use the current sun.tex and sst.tex templates
- Renamed sun109fig.ps figure to sun109_cover.eps
- Rename main.gif to sun109_main.gif
datacube: For sc/16 use PNG files since they are all screen grabs anyhow
datacube: For sun/237 use PNG files since they are all screen grabs anyhow
SC/15: Forgot to copy PNG images to HTX directory (add to .htx_tar.extras)
kappa: Switch to pdflatex

Remove sun95_*.gif files as they were poor copies of the screen grabs
and the embedded PDFs are better. In theory we could simply convert
the screen grab PDFs to PNG but I will save that for later. In future
we should just screen grab in PNG and use that natively for the PDF.

Converted example GIF files to PNG.

Latex file no longer has special section for GIF.
pisa: Use PNG cover image instead of GIF
photom: SUN/45 to pdflatex

Remove GIF version of cover image.
pongo: Use PNG instead of GIF
polpack: Replace GIF with PNG versions

Some of these PNG files could be used directly instead of PDF when
we convert to pdflatex
pongo: Actually remove GIF files
star2html: Convert PDF images to PS and copy PNG files

latex2html can not handle PDF embedded images and it will be quite
a hack to fix this. Currently latex2html runs latex so that all
the includegraphics options are processed properly. It then converts
the DVI file to postscript files (one file per "page") and uses
pstoimg (ghostscript and netpbm) to convert the output PS files
to PNG images. Converting this to pdflatex and adjusting pstoimg
to convert the PDF pages to images is not a completely crazy job
but it seems a big enough change that it would make the Starlink
copy of latex2html completely different and there is no obvious
place to send the patches upstream.

For now star2html will scan the tex file for includegraphics lines
and determine if any PDF files are being embedded. If they are it
runs pdf2ps and converts them to postscript so that the standard
mechanism will work. Star2html will complain if the
includegraphics directive includes an explicit pdf suffix as that
will break the conversion within latex2html.

latex2html can locate PNG files in includegraphics lines so long
as the files are in the current directory. Star2html does the conversion
in a temporary directory and assumes that images will be noted
explicitly with \htmladdimg and mentions in .htx_tar.extras files. This
means that includegraphics will not work for PNG. To overcome this
star2html now scans the tex file and copies relevant PNG files into
the working directory.
sun249: Add extras file to ensure PNG images are copied into HTX dir
docs: SG documents - replace EPS files with PDF files