Libuv

[TimWhiting]

Implemented: (Low Level, Callback, LibUV wrapper)
Streams
File I/O
Net / TCP I/O
Timer
FS Poll
FS Event
Signals
TTY

Implemented: Async API
Basic File I/O
Basic TCP I/O
Timer (Also implemented for js and wasm)

Implemented: llhttp parser

Missing LibUV: UDP, Threading, Process, uv async channels, Prepare/Check/Idle

Missing (external libraries): SSL!

[TimWhiting]

Here is one major change. Adding event loop to the core effects.
The async library requires that there be an event loop around it, or at the very least a timer that can call callbacks.

In principle we could just use an implicit parameter for the handler for the async effect, to get the event loop and wrap it.

The problem with that approach is that if you use any libuv apis directly in callback style without the async library then you have to manually remember to initialize the event loop.
We could in principle make a custom error and detect uninitialized event loops at runtime, but that would introduce runtime overhead for each libuv call that uses callbacks, so I opted to create this new effect instead.

I will note that I did use the implicit parameter approach for the timer requirements of the async lib so that in principle you can swap out the libuv library for some other event loop library.