REPL unblock event loop AND fix REPL setTimeout fire problems

[kevinkassimo]

Closes #1161 .

• Unblocks event loop by making REPL async
• Fix op_repl_readline always blocking problem that breaks setTimeout fire
• Add setTimeout test

/cc @hayd @cedric05

Also, though not fixed in this PR, there is one more issue I found that might need to be address later:

deno/src/resources.rs

Lines 335 to 345 in 89096c9

	pub fn readline(rid: ResourceId, prompt: &str) -> DenoResult<String> {
	let mut table = RESOURCE_TABLE.lock().unwrap();
	let maybe_repr = table.get_mut(&rid);
	match maybe_repr {
	Some(Repr::Repl(ref mut r)) => {
	let line = r.readline(&prompt)?;
	Ok(line)
	}
	_ => Err(bad_resource()),
	}
	}

Since let line = r.readline(&prompt)?; is blocking, this might cause RESOURCE_TABLE.lock() not released in REPL and blocks other resources reads and writes

[ry]

Nice! Looks good - just one comment.

[ry]

Also please split the commits into e5f204f and yours.

[ry]

LGTM

[hayd]

This could be done with the existing input method, without "special treatment" 😄, and avoid the repetition. I will make a separate PR.