async+perf: ch6, more on 'context is king'
async+perf: ch6, minor tweak in wording
async+perf: lots of great tweaks/improvements from @kriskowal, closes #259
async+perf: ch6, added section 'engine optimizations'
async+perf: ch6, working on 'jsperf' section
async+perf: ch6, more on 'jsperf.com'
async+perf: ch6, reorg of some discussion, clarifications
async+perf: ch6, more on jsperf