[URI Template] Refactor expansion to use regex
[URI Template] Refactor expansion to use regex

kylef/URITemplate.swift,kylef/URITemplate.swift,RuiAAPeres/URITemplate.swift,RuiAAPeres/URITemplate.swift,mogstad/URITemplate.swift,mogstad/URITemplate.swift,RuiAAPeres/URITemplate.swift