PEP 394 & cleaner code after webhost upgraded to py2.7

Ugly .replace() rather than .format() syntax was introduced
in 5dbf81ae8eff565269df91b2a63610a25d0fad6c to work around
the project's webhost being on Python 2.5 at the time.

Also explicitly specify that this is Python 2 to meet PEP 394;
this wasn't originally in place because it also didn't work
on the previous webhost setup.