[Templates] Encoding patch for Provider

[Andy Wardley]

Tom Insam wrote:
> will encode the output to utf-8 before writing. Andy - as regards your
> reply, I think it would be a bad idea to assume the same input and
> output template character sets. But that's just me.

Having looked it over, I agree.

It's a more complex issue than I first thought.  I've changed ENCODING
to only specify the default encoding for input templates.  It doesn't
have any effect on the output encoding - you still have to do that 
via the fourth process() argument.

I'll try and address the whole encoding isse more rigorously for TT3.

A