Auto merge of #37497 - iirelu:proper-vec-brackets-2, r=steveklabnik

Make all vec! macros use square brackets: Attempt 2

[The last PR](rust-lang/rust#37476) ended with tears after a valiant struggle with git. I managed to clean up the completely broken history of that into a brand spanking new PR! Yay!

Original:

> Everyone hates the old syntax. I hope. Otherwise this PR has some controversy I wasn't expecting.

> This would be the perfect time to write a lint recommending vec![..] when you use another style.

> Disclaimer: I may have broken something. If I have, I'll fix them when the tests come in. Luckily the chance for a non-syntactical error is pretty low in all this.

lib.rs

@@ -58,7 +58,7 @@
 //! struct Edges(Vec<Ed>);
 //!
 //! pub fn render_to<W: Write>(output: &mut W) {
-//!     let edges = Edges(vec!((0,1), (0,2), (1,3), (2,3), (3,4), (4,4)));
+//!     let edges = Edges(vec![(0,1), (0,2), (1,3), (2,3), (3,4), (4,4)]);
 //!     dot::render(&edges, output).unwrap()
 //! }
 //!
@@ -164,8 +164,8 @@
 //! struct Graph { nodes: Vec<&'static str>, edges: Vec<(usize,usize)> }
 //!
 //! pub fn render_to<W: Write>(output: &mut W) {
-//!     let nodes = vec!("{x,y}","{x}","{y}","{}");
-//!     let edges = vec!((0,1), (0,2), (1,3), (2,3));
+//!     let nodes = vec!["{x,y}","{x}","{y}","{}"];
+//!     let edges = vec![(0,1), (0,2), (1,3), (2,3)];
 //!     let graph = Graph { nodes: nodes, edges: edges };
 //!
 //!     dot::render(&graph, output).unwrap()
@@ -226,8 +226,8 @@
 //! struct Graph { nodes: Vec<&'static str>, edges: Vec<(usize,usize)> }
 //!
 //! pub fn render_to<W: Write>(output: &mut W) {
-//!     let nodes = vec!("{x,y}","{x}","{y}","{}");
-//!     let edges = vec!((0,1), (0,2), (1,3), (2,3));
+//!     let nodes = vec!["{x,y}","{x}","{y}","{}"];
+//!     let edges = vec![(0,1), (0,2), (1,3), (2,3)];
 //!     let graph = Graph { nodes: nodes, edges: edges };
 //!
 //!     dot::render(&graph, output).unwrap()