Copy-editing the "Arrow Functions and their scope" article

Fixed some typos, ambiguities, improved formatting.

Please take a look, but don't merge yet until the comments marked as TODO are resolved. I need some feedback/discussion on the TODOs.

Also, as I'm using inline code blocks (backticks), this PR is blocked by #7.
Merge branch 'src-arrow' of github.com:UltCombo/es6rocks.github.io into UltCombo-src-arrow
Merge branch 'UltCombo-src-arrow' into src