Refactor to use frozensets and whitespace codepoints on Py3
Refactor to use frozensets and whitespace codepoints on Py3

vladmunteanu/hyper-h2,bhavishyagopesh/hyper-h2,vladmunteanu/hyper-h2,Kriechi/hyper-h2,Kriechi/hyper-h2,python-hyper/hyper-h2,python-hyper/hyper-h2