Macros

[VincentRPS]

Add support for syntactic macros. These are almost like functions which intake syntax
and output different syntax during compilation. Macros should be a front-middle end process
and shouldn't involve the backend with anything other than codegen.

[elenakrittik]

We need to decide whether supporting macros-by-example is worth it. Given the tooling/support level we are aiming to provide to procedural macros, it may be better to implement support for easily making MBE-style macros inside procedural macros. For example, instead of writing

macro print_many($($arg:expr),*) {
	$(
		print($arg);
	),*
}

One could instead write something like

import std::syntax::{Syntax, syntax, lexer::Delimiter, parser::{parse_delimited, parse_expr}};

macro print_many(syntax: Syntax) -> Syntax {
	parse_delimited(Delimiter::Comma, parse_expr)
		.map((expr) => syntax! { print($expr); })
		.collect()
}

(Syntax is something akin to TokenStream in Rust, and syntax! is very similar to the quote macro of the quote Rust crate)