doc(recipes/identifier): convert to greedy parser

[sno2]

Basically, the current recipe for identifier is greedy and likes to take everything that it can and silently stop if it sees something it doesn't like (i.e. whitespace). However, I think it would be a lot better to just make it check the entire string to be a valid identifier and just make use of the multispace1 or any other delimiters you want ((, ), ect.) surrounding the identifier when using it within a different parser (i.e. variable initialization as stated in the docs added). This should make it easier to use because I actually had a big bug that I didn't realize was there until later from the identifier saying it's valid when it's not because it requires you to check if the rest of the input (input, parsed) is empty.

Tests I used:

#[cfg(test)]
mod tests {
  	#[test]
	fn fn23() {
		function("let foo;").unwrap();
		function("let _asdf23;").unwrap();
		function("let 23asdf;").expect_err("Can't begin with numbers");
		function("let a\nnb;").expect_err("Can't have newlines");
	}
}