Rust quasi-quoting macro.

Example

Here is a simple example to build the syntax::ast::Expr that represents adding two numbers together:

```rust

![feature(plugin, rustc_private)]

![plugin(quasi_macros)]

extern crate syntax; extern crate quasi;

use syntax::ext::base::ExtCtxt;

fn makeextctxt(...) -> ExtCtxt { ... }

fn main() { let cx = makeextctxt(...); let expr = quote_expr!(cx, 1 + 2);

// prints `1 + 2`.
println!("{}", syntax::pprint::expr_to_string(&expr));

} ```