async+perf: ch3, wording tweaks
async+perf: ch3, promise patterns
Typo Fix: overriden > overridden
Typo Fix: ther > the
Typo Fix: assigment > assignment
Typo Fix: statment > statement
Typo Fix: verions > versions
Typo Fix: aribitrarily > arbitrarily
Typo Fix: concesssion > concession
Typo Fix: sytnax > syntax