Correctly implement Redirect feature

[8eecf0d2]

This is a pretty insane feature considering what it's called, what it's actually capable of, and how it's implemented...

Notice: It's confusing and important to understand if the "redirect rule" in question is a true 3xx style redirect or a more fancy rewrite.

The main features to implement:

• Traditional Redirect
• Traditional Rewrite (to filesystem / build.publish)
• Proxy Rewrite
• Placeholder / Pattern matching

Redirect Features

Basic Redirects / Rewrites, Http Status Codes

Netlify will return status code 301 for what it calls basic redirects.
Netlify will perform a rewrite if a status code is set and not equal to 301, 302, 303.

• Support "basic redirect"
• Support "basic rewrite"

Custom 404

By default Netlify will serve a 404.html file if it's provided and no redirect rules or static files match the path.

• Support for custom 404.html

Trailing Slashes

I'm not even gonna bother with this yet...

Placeholders

Basically param swapping between from and to - should be easy enough to implement with express and a url pattern library.

from = "/:partA/:partB"
to = "/:partB/:partA"
# "/foo/bar" → "/bar/foo"

• Support placeholder / pattern replacement

Splats 🤦‍♀️

Similar to placeholders except the * and :splat param are bound.

• Support special splat placeholder

Query Params

More or less states that query params can be used as placeholders, the syntax is weird but toml is luckily more readable that Netlify's _redirect file formatting.

• Support query placeholder

Hostnames & Protocols, GeoIP & Language

These feature are getting way beyond my personal use cases - plus I don't see them being entirely useful for local development, it'd be great to support them but I'm not holding my breath.