Fixes

• Simplify and fix assertion (#1033)
• Only pause on >=200 body (a48f9f0)
• BodyMixin.arrayBuffer Buffer -> ArrayBuffer typedefs (#1025)
• FormData.set empties this[kState] if k exists (#1017) …
• Prioritize host header (#1007)
• Fetch response body may be undefined

Improvements

• Add blocking request option (#1034)
• Add experimental diagnostics channel (#1000)
• Improve code coverage of lib/fetch/headers.js (#1027)
• Avoid duplicate require (#1023)
• Add onInfo option (#977)