Rename arena.png to arena_caddy.png

This is the marked up arena map.
Resize arena_caddy.png to fit with 800x600px
Add official arena map to the intro section
Fix unclosed <em> tag
Spell check fixes
Makefile support to export .png version of all .dia files
Add line_tracking.dia and caddy_in_arena.png
Simplify duplicated calculations
Add customized latex header

Generated with:

doxygen -w latex header.tex footer.tex style.tex
Fix header so that secions are numbered properly

For some reason the output of `doxygen -w` does not match what is found
in a refman.tex that is generated without custom LATEX_HEADER option.
WIP snapshot of PID line tracking updates