Static Generation / SSG Improvements

Allow Next.js to become fully hybrid by providing methods to do both static generation and server-side rendering on a per-page basis.

• Two new data per-page fetching methods
  • getStaticProps – Opt-in to static generation (SSG) at next build time.
  • getServerProps – Opt-in to server-side rendering (SSR) which renders on-demand.
• A new method for statically generating (SSG) a set of routes from dynamic sources
• getStaticPaths – Return list of parameters for dynamic routes to do static generation (SSG)