async+perf: cleanup of org/TOC, starting on 'microperformance' discussion
fix small typo
async+perf: ch6, lots more on microperformance, 'TCO', etc
Merge pull request #266 from masak/patch-2

fix small typo
async+perf: finishing up ch6 finally
async+perf: revisions per #251
async+perf: ch4, tweaks and clarifications to wording. also day 365 of the streak. :)
async+perf: ch4, adding discussion of generator 'return()', closes #260
async+perf: ch4, minor wording tweaks for clarification
async+perf: ch4, corrections to iterator 'return()' behavior, clarifications
types+grammar: adding 'reserved words' section to apA, closes #267
types+grammar: adding 'implementation limits' section to apA, closes #210
types+grammar: adding /be quotes about ASI, closes #265
types+grammar: adding 'try..finally' discussion to ch5, closes #268
types+grammar: minor tweaks to add clarity, format code
types+grammar: per @ljharb adding discussion of throw inside a finally
types+grammar: further clarification of finally about explicit vs implicit 'return'
types+grammar: clarification notes about labeled loops behavior
types+grammar: more clarifications around labeled blocks
types+grammar: more clarifications about 'finally' and labeled blocks