Use new syntax of url built-in template tag.

The syntax changed to wrap the main argument in quotes (to be consistent
with other Django template tags it seems). This is optional in Django 1.3
and 1.4, but mandatory in the recently released Django 1.5.

After this commit you must be running Django 1.3 or later.

Closes #52.
getLaTeXScientificNotation() now handles negative numbers correctly.

Previously it would fail for negative numbers due to the need to take the
logarithm of the value to get the exponent.
Added "load url from future" to every template file.

I had hoped that I would be able to get away with just adding it to the base
template file, but no dice. This should make the website work once again
with Django 1.3 and 1.4. (1.5 and later do not require this line, but it
also does not harm anything to have it present.)