types+grammar: appendixA, fixing code typo, per @qgustavor
async+perf: starting ch4 'generators'
async+perf: ch4, starting 'breaking run-to-completion' section
Fixed a tiny typo
Merge pull request #212 from HugoGiraudel/patch-1

Fixed a tiny typo
async+perf: starting 'input + output' section
async+perf: ch4, more on 'iteration messaging' and 'tale of two questions'
async+perf: ch4, tweaks and clarifications