Fixed broken slide(undef) behavior
Brush up on docs, especially for toc_width
Added toc_font_ratio and friends
Added an ignore file
Postscript printing now uses Subcanvas
footer accessor now correctly handles setting the footer
A slew of font size fixes
Improve per-slide font-size-factor handling
Vastly expanded Prima::Talk documentation; revised the stashing system.

The documentation now discusses slide construction and transitions at
great length (though content types still need lots of work).

While going through the means for specifying dynamic content, I realized
how I could more intelligently update the data stashing mechanism. It
now works via AUTOLOAD. It is both easier to use and generally cleaner.
Added StretchyImage widget; still needs docs and tests
Added inteligent default size handling to StretchyImage
Add filename handling to StretchyImage
Add has_image method to StretchyImage
Fix filename handling in StretchyImage
Revised Prima::Talk to use Prima::StretchyImage
Added %colheightleft size spec, and fleshed out size spec docs and implementation

The documentation was left unfinished for the size specifications.
Furthermore, the custom size spec handling was only partially
implemented. This commit finishes the documentation and finalizes
the implementation. It also adds the %colheightleft size spec. The
speck only pays attention to packed widgets, so it could make
mistakes, but it properly handles packing on the bottom or top
of the container.