Fix typo in readme example.
exts: Know the SVG type.

It's fixed by W3C. Chrome might not especially like it, but Chrome can suck
it. (Actually, it works fine for standalone SVGs, just not for fonts.)
main, parts: Include templaters in list of acceptable MIME types.

This fixes a bug where a MIME type not in the list of default templaters (SVG
in this case) would never be used, even if a custom templater was registered
for it.

Look up the available templaters at worker time, when formatting happens. This
ensures that any view-specific templaters are visible, and that nothing gets
left out of the decision to use a certain MIME type.
0.3.2, with an important bugfix.