Changed stability annotations for the new Error and Display impls
for std::ffi::FromBytesWithNulError as they aren't subject to
stability the same way.

…m::TokenTree::Sequence`.

Simplify `TokenTree` and fix `macro_rules!` bugs

This PR
 - fixes rust-lang#39390, fixes rust-lang#39403, and fixes rust-lang#39404 (each is a [breaking-change], see issues for examples),
 - fixes rust-lang#39889,
 - simplifies and optimizes macro invocation parsing,
 - cleans up `ext::tt::transcribe`,
 - removes `tokenstream::TokenTree::Sequence` and `Token::MatchNt`,
   - instead, adds a new type `ext::tt::quoted::TokenTree` for use by `macro_rules!` (`ext::tt`)
 - removes `parser.quote_depth` and `parser.parsing_token_tree`, and
 - removes `quote_matcher!`.
   - Instead, use `quote_tokens!` and `ext::tt::quoted::parse` the result with `expect_matchers=true`.
   - I found no outside uses of `quote_matcher!` when searching Rust code on Github.

r? @nrc

…excrichton

impl RangeArgument for RangeInclusive and add appropriate tests

Now that `RangeArgument` returns a `Bound`, the impl for `RangeInclusive` is natural to implement and all that's required are tests around it.

…=frewsxcv

Improve associated constant rendering in rustdoc

Before:

<img width="1440" alt="screen shot 2017-02-19 at 00 30 51" src="https://cloud.githubusercontent.com/assets/3050060/23097697/caeed80e-f63a-11e6-98c2-5d27e4efd76d.png">

After:

<img width="1440" alt="screen shot 2017-02-19 at 00 30 39" src="https://cloud.githubusercontent.com/assets/3050060/23097698/cfb4874e-f63a-11e6-80cf-ffbf5c5c6162.png">

cc @SergioBenitez

r? @rust-lang/docs

added Error and Display impl for std::ffi::FromBytesWithNulError

Fixes rust-lang#39925.

This is my first PR, so I wasn't quite sure about the stability annotation.

…excrichton

impl FromIterator<&char> for String

Move two large error_reporting fn's to a separate file

Hello!

I tried to make `librustc/infer/error_reporting,rs` more readable by modularizing it and moving its two largest functions to a separate file.

If you have any suggestions, please send it right away! 🚀

Thanks goes to @nikomatsakis for supporting.