Quote misc

[graydon]

This gets the new token-tree quasiquoter up to the point of being able to stand in for of #ast in the pipe protocol compiler; #ast is only there in #[cfg(stage0)], whereas it's quote_expr! and quote_type! in #[cfg(stage1)] and [#cfg(stage2)]. Also makes the splicing machinery much more robust and extensible (you are allowed to splice anything that implements ToTokens).

While this looks like a lot of sound and noise for nothing, it enables (post-snapshot) cutting out substantial portions of the redundant macro machinery in the frontend. #ast and the quasiquoter is sort of the last thread holding it in place (from last summer).

[graydon]

r? @brson

[brson]

Awesome work. r+

[graydon]

This landed in bcde593