Fix stumbling points

[timoxley]

• Fix bug in filter example
• Make simpler reduce exercise to introduce concept
• Add a chaining example with all functions supplied, just need to chain them up
• Hint at chaining with .filter() and .map() in basic-filter exercise. (may be redundant if do previous item)
• Make arguments/apply exercise to introduce Array.prototype.slice
• Explain map/reduce/filter etc in the text and give an example as the simple mdn examples are hard to find or non-existent.
• New exercise for Function.bind/call/apply and this
• Remove second argument to map callback in reduce exercise or explain it better
• Specify no for loops or additional functions required unless in boilerplate
• Explain run/verify/menu process better?
• Explain every method required for every exercise.