auto merge of #8031 : graydon/rust/emacs-mode-rewrite, r=catamorphism

The previous mode did a lot of very manual char-at-a-time parsing and was quite fragile and difficult to maintain. I talked to Marijn and he suggested I'd have better luck just rewriting it from scratch. This is the result of that effort; it seems to be faster, a bit easier on the eyes and more-or-less as well behaved when indenting. The algorithm is a bit different I suspect (it was hard to tell the previous one) but I tried to keep it simple and pleasant-looking.

src/etc/emacs/README.md

@@ -13,21 +13,8 @@ file:
     (add-to-list 'load-path "/path/to/rust-mode/")
     (require 'rust-mode)
 
-Make sure you byte-compile the .el files first, or the mode will be
-painfully slow. There is an included `Makefile` which will do it for
-you, so in the simplest case you can just run `make` and everything
-should Just Work.
-
-If for some reason that doesn't work, you can byte compile manually,
-by pasting this in your `*scratch*` buffer, moving the cursor below
-it, and pressing `C-j`:
-
-    (progn
-      (byte-compile-file "/path/to/rust-mode/cm-mode.el" t)
-      (byte-compile-file "/path/to/rust-mode/rust-mode.el" t))
-
-Rust mode will automatically be associated with .rs and .rc files. To
-enable it explicitly, do `M-x rust-mode`.
+Rust mode will automatically be associated with .rs files. To enable it
+explicitly, do `M-x rust-mode`.
 
 ### package.el installation via Marmalade or MELPA
 
@@ -67,24 +54,6 @@ should upgrade in order to support installation from multiple sources.
 The ELPA archive is deprecated and no longer accepting new packages,
 so the version there (1.7.1) is very outdated.
 
-#### Important
-
-In order to have cm-mode properly initialized after compilation prior
-to rust-mode.el compilation you will need to add these `advices` to
-your init file or if you are a melpa user install the `melpa` package.
-
-```lisp
-(defadvice package-download-tar
-  (after package-download-tar-initialize activate compile)
-  "initialize the package after compilation"
-  (package-initialize))
-
-(defadvice package-download-single
-  (after package-download-single-initialize activate compile)
-  "initialize the package after compilation"
-  (package-initialize))
-```
-
 #### Install rust-mode
 
 From there you can install rust-mode or any other modes by choosing