Port code to use ext-encoding

[dktapps]

this is a test run to see what it's like to work with the new API.

So far, it seems to be OK, although I keep forgetting the parameters for the static methods, which is annoying. Instinctively I'm reaching for instance methods, and I have to keep reminding myself why I chose to implement the new API this way instead of using instance methods (it's because this design is more resistant to mistakes).

Haven't tested this yet. Fine to ignore the test errors (it's just because the extension isn't present).