* Port to Babel 7
Use the Babel 7 @babel/core transpiler, falling back to the older babel-core version if possible.
* Use Babel 7 and preset-env 7 to build the browser compiler and test Babel transpilation
* Update docs for Babel 7
* Upgrade Babeli (now babel-minify) which fixes the bug that was forcing us to run Babel twice for transpilation
* Add --transpile option (WIP)
* Node API always compiles a string, so it doesn’t need the option to pass a path to an options file, it can always just pass an object to `transpile`; get `transpile` working with `eval`
* Not allowing argument to `--transpile` so don’t need to cover so many cases
* Don’t need to worry about `sourceMaps` option to pass to Babel, `inputSourceMap` overrides it
* Rewrite Webpack test to use Node API
* Make the compiler safe again for browsers and Webpack/Browserify
* Node version of CoffeeScript.compile passes reference to Babel if transpile is requested
* Test Node API for transpile option
* Test for merged source maps
* Test for Node API error message
* Only stop searching for Babel options if a package.json has a truthy "babel" key
* Update docs
