Changed all PlantUML rules to use -pipe ...

This seems to work more consistently with include files.
It also removes the need to rename LaTeX output files.

• Set up global, self-deleting temporary directory to use in situations where tools can’t be pipelined together (closes #5). ...

• Added mktemp command to configuration to support the above.

• Reverted SVG to PDF conversions back to Inkscape, as it seems to do a better job of fonts than rsvg-convert, and the eariler performance issues appears to have been fixed.

• Corrected --jobname to -jobname for LaTeX commands (although it worked anyway).

• Added a pdfcrop to the end of PlantUML → SVG pipeline, as different converters don’t always crop the output.

• Simplified commands to generate faded images, as the old version using composite stopped working for no readily apparent reason.

• Added standard variables PAPER_INCLUDE_PATH and LATEX_INIT_FILE and rewrote all LaTeX-generating XSLT calls to use these. ...

• Revised passing of XSLT parameters to remove arbitrary limit on number of parameters.
• Synced up debug variables across different make include files.
• Fixed some raw calls to various commands.

• Added first cut at PlantUML rules.

• Switched to rsvg-convert from Inkscape, as Inkscape has become horribly slow (too many fonts, perhaps?). rsvg-convert comes with librsvg.

• Removed paper year from paper-include-path value, as not everyone will have their paper trees organised by year. Safer to assume that the paper root directory exists at the top level of $(ALL_PAPERS_ROOT); use symlinks to achieve this if not.

• Added paper-include-path stylesheet parameter to (Xe)LaTeX rules.

• Removed now-obsolete LaTeX option variables; these have been replaced by explicit LaTeX options embedded within the XML document itself.

• Added a PDF to PDF (rename) rule. (Surprised we never had one before now!)

• Added conditionals to enable building of PDF from LaTeX using XeLaTeX.

• Switched to using \def instead of \newcommand for pre-\begin{document} definitions, as it seems safer.

• Changed the way that LaTeX document class options are handled.

• Restored --export-text-to-path to Inkscape options for PDF output to eliminate aliasing.

Removed now obsolete CVS substitutions.

Added support for Sass → CSS.

Fixed file permissions.

- Corrected paper-period argument to period-code.

- Fixed buggy calls to convert_normal function. ...

- Removed superfluous backquotes from function bodies.

- Corrected a comment.

- Refactored rules for converting bitmap images to support multiple prerequisite ...

file types.
- Added rules for zoomed PNGs for use when drop shadows cause the SVG to PDF
  conversion to freak out.

- Added XCF to PNG conversion.

- Added some intermediate file cleanup for blurred background image generation.

- Added rule to export PNG with transparent background from Inkscape.

- Added Unicode switch support.

- Added support for new paper-year and paper-period stylesheet parameters. ...

- Fixed an unnoticed typo in the standard rules for generating LaTeX and
  HTML from XML. Obviously they've never been used!

- Removed old "department" and "paper" stylesheet parameters in favour of ...

"subject-code" and "paper-number" (which were already in place anyway).