async+perf: ch5, 'asm.js' finished
async+perf: changes per PR from @PeterJensen, cleanup, closes #254
async+perf: cleanup of text in 'asm.js' section
async+perf: ch5, fixing spelling, prolyfill -> prollyfill, closes #255
async+perf: toc/readme update
async+perf: starting work on ch6, with 'benchmarking' section
updating root README