This commit changes the `Deno.serve` function signature to be more
versatile and easier to use. It is now a drop in replacement for
std/http's `serve`.
The input validation has also been reworked.
- Merge "Deno.serve()" and "Deno.serveTls()" API
- Remove first argument and use "fetch" field options instead
- Update type declarations
- Add more documentation
