Better macro support

[udoprog]

This reworks the Query system so that it can be passed around statically, and adds support for performing constant evaluation in macros. That means that the following (or any constantly evaled expressions) will work without issues:

const FORMAT_STRING = build_format_string("Hello");

const fn build_format_string(prefix) {
    `{prefix} \{\}`
}

fn main() {
    println!(FORMAT_STRING, "World"); // -> will produce "Hello World"
}

Note that the current state of the println! macro is still only a skeleton, i.e. arg parsing hasn't been implemented yet. But right now it can receive a constant value as the first argument.

I've also reworked template strings so that they solely are lexer sugaring over a different kind of expression which uses a new reserved keyword template. That means that this:

`Hello {world}`

Desugars to this during lexing:

template { "Hello ", world }

This makes it vastly easier to work with template string in macros, since the desugared version uses syntax which works well with Rust and the quote! macro.