Fix output of `yield *`

• Fix JS output routine which (incorrectly) removed the asterisk from yield *.
• Improve syntax testing to catch differences in primitive values in ASTs

Fix output of `a || (()=>b)`

Fix JS output routine which (incorrectly) removed parenthesis from a || (()=>b) causing a precedence problem.

Closes #54

Fix issue with `for..of` with a `const` or destructuring initializer

• Fix issue with for..of with a const or destructuring initializer
• Optimize EagerThenable and guard multiple Promise resolutions

Fix complex ES6 destructring, export async function

• Fix issue with non-trivial destructuring assignments (fixes MatAtBread/fast-async#8 - thanks to @simonbuchan)
• Fix case where empty "else" block throws an exception (fixes #50 - thanks to @Antender)
• Fix case where single line exported function was incorrectly hoisted with no reference (fixes MatAtBread/fast-async#7 - thanks to @simonbuchan, @naturalethic and @nightwolfz)
• Bump acorn to v3.3.0

Fix `export async` and non-strict block-scoping

• Update acorn-es7-plugin to fix issue with export async in webpack
• Fix edge case where a continuation function is treated as a block-scoped (breaks some constructs in non-strict Safari as it could have generated function declarations inside a block).

Enhance support for 'engine' mode

• Optimize case where 'engine' generates an 'awaitAnywhere' Promise-style callback for an async function nested inside a sync function, and await is legal.
• Bump version to make support for 'engine' mode easier to detect in toolchains.

"Engine" mode for JS engines that implement async & await

• Add 'engine' mode that only transpiles the nodent ES7 extensions (async get x(){}, async throw x, async return and await anywhere). Standard ES7 async/await constructs are passed through the compiler unchanged to be run by the underlying engine (e.g. Chrome v53 or Edge v14).
• Implement parsing for proposed ES7 Object spread var {a,b,...x} = y ; used in Babel (see MatAtBread/fast-async#6)

Revert change to runtime inclusion in 2.5.8 as it breaks some live uses of browserify/webpack

Revert change to runtime inclusion in 2.5.8 as it breaks some live uses of browserify/webpack, and was only included to make istanbul work

ES6 let and const scoping and minor fixes

• Implement ES6 declaration hoisting
• Fix typo in covers/https to prevented get() from working
• Fix path resolution for nodent.require(...) built-ins
• Fix typos when defining writable Object properties
• Implement "dual-mode" tests that compare sync/async routines directly
• Maintain the position of directives when asynchronizing blocks
• Add dual-mode tests for consts in struct & sloppy mode and scoped try test
• Correct case where await is at the top level in generator mode
• Avoid exception when node is created with no location info
• Include eager.js into runtime.js as source to make istanbul coverage tests work
• Bump acorn-es7-plugin

Fix `this` in loops. Fix CLI option.

• Correctly bind this inside loops if it is referenced (#39). Many thanks to https://github.com/jeffreylin for the test case and fix.
• Fix command-line option --use=(mode) with text input
• Bump acorn-es7-plugin to to 1.0.15