Update frequently asked questions in documentation

[Nutlope]

This is a rewrite of the FAQ section as it's quite outdated. Thank you to @styfle and @leerob for the suggestions.

Here's a list of changes I've made:

• Removed “How big is it”
• Removed “What syntactic features are compiled? How do I change them?”
• Replaced all occurances of "it" with "Next.js"
• Changed "Is Next.js production ready?" to mention showcase
• Started the answer to each question with either yes or no for yes/no questions
• Listed more pros for router section, changed question name, and backlined to migrating from react router docs
• Revamped "fetching data" answer to list all our data fetching methods and backlink to docs
• Made "Can I use Next.js with my favorite JavaScript library?" more clear and emphasized the large number of examples we have
• Reorganized questions to make more sense
• Made wording more consistent throughout

Additional Questions:

1. Do we want to keep the "What inspired Next.js" section the same? One option could be to only keep the first sentence linking to G's article and not talk about PHP because of its reputation among newer web developers as an old & outdated technology.
2. What's the advantage of routes always being lazy-loadable? I'd like to add this to the last bullet point of the new router question to make it obvious what the benefit is.

[leerob]

Excellent incremental updates, thank you!