Figure sizes for DITA output to PDF

We will be having some people using FOP and others using XEP to generate PDF files. It's actually quite difficult to set the width and height attributes of figures so that graphics look good in both formats. Here are some recommendations:
- FOP and XEP only have a very limited number of supported formats in common: GIF, JPEG and PNG for bitmaps and SVG for vectorials.
- Only specify the width. The DITA-OT will then calculate the height automatically so as to preserve the original aspect ratio.
- Specify the width in "real" width units, for example "10mm" or "3in".
- For vectorial graphics, specify the same width value for all graphics to obtain a cleaner output. In the old FrameMaker template, the main text column was 135mm wide, so this is a good value to use.

So, for example:
<fig>
<img align="right" width="135mm" placement="break" href="architecture.svg"/>
</fig>