auto merge of #12783 : adrientetar/rust/more-docs, r=alexcrichton

- remove `node.js` dep., it has no effect as of #12747 (1)
- switch between LaTeX compilers, some cleanups
- CSS: fixup the print stylesheet, refactor highlighting code (2)

(1): `prep.js` outputs its own HTML directives, which `pandoc` cannot recognize when converting the document into LaTeX (this is why the PDF docs have never been highlighted as of now).

Note that if we were to add the `.rust` class to snippets, we could probably use pandoc's native highlighting capatibilities i.e. Kate ([here is](http://adrientetar.github.io/rust-tuts/tutorial/tutorial.pdf) an example of that).

(2): the only real highlighting change is for lifetimes which are now brown instead of red, the rest is just refactor of twos shades of red that look the same.
Also I made numbers highlighting for src in rustdoc a tint more clear so that it is less bothering.

@alexcrichton, @huonw

Closes #9873. Closes #12788.

src/etc/licenseck.py

@@ -33,8 +33,6 @@ license4 = """ The Rust Project Developers. See the COPYRIGHT
 """
 
 exceptions = [
-    "doc/lib/codemirror-node.js", # MIT
-    "doc/lib/codemirror-rust.js", # MIT
     "rt/rust_android_dummy.cpp", # BSD, chromium
     "rt/rust_android_dummy.h", # BSD, chromium
     "rt/isaac/randport.cpp", # public domain