Convert link to function component (#14633)
Convert link to function component (#14633)

Convert `Link` to a function component. Prefetch logic and memoized url formatting now meshes nicely with React hooks. Class methods were hoisted to module scope to preserve performance characteristics.
azukaru/next.js,azukaru/next.js,flybayer/next.js,zeit/next.js,azukaru/next.js,JeromeFitz/next.js,zeit/next.js,flybayer/next.js,JeromeFitz/next.js,zeit/next.js,JeromeFitz/next.js,JeromeFitz/next.js,azukaru/next.js,flybayer/next.js,flybayer/next.js