Add @Spell clusters to Vim syntax file

Add @Spell clusters to Vim syntax highlighting file to do spell checking
only inside comments and strings
added empty() to Peekable
Removed remnants of `@mut` and `~mut` from comments and the type system.
extra::ebml: Make reader::Res public

Since reader::vuint_at() returns a result of type reader::Res it makes sense
to make it public.

Due to rust's current behavior of externally referenced private structures,
https://github.com/mozilla/rust/issues/10573, you could still use the result and
assign it to a variable if you let the compiler do the type assignment,
but you could not explicitly annotate a variable to hold a reader::Res.
extra::ebml: Add unit test for vuint_at()
ebml::extra: Optimize reader::vuint_at()

Use a lookup table, SHIFT_MASK_TABLE, that for every possible four
bit prefix holds the number of times the value should be right shifted and what
the right shifted value should be masked with. This way we can get rid of the
branches which in my testing gives approximately a 2x speedup.
libsyntax: Make managed box `@` patterns obsolete
xfail another native test on android (#11419)
auto merge of #11518 : brson/rust/moreandroidxfails, r=alexcrichton
librustc: Remove `@` pointer patterns from the language
auto merge of #11305 : pcwalton/rust/at-patterns, r=pcwalton

r? @nikomatsakis
librustc: Don't allow use after move of implicitly coerced object. Fixes #11481.
librustc: Don't translate an expr twice when implicitly coercing to a trait object. Fixes #11197.
auto merge of #11525 : luqmana/rust/trait-coercions, r=pcwalton

Fixes 2 annoying issues with implicit trait object coercion: #11481 & #11197.
mk: Make TESTNAME and VERBOSE work with android. Closes #10957
std: Ignore bind error tests on android. #11530
auto merge of #11531 : brson/rust/yetmoreandroidfixes, r=alexcrichton
dox: Write a guide to the rust runtime
auto merge of #11501 : alexcrichton/rust/dox, r=brson

The official documentation sorely needs an explanation of the rust runtime and what it is exactly, and I want this guide to provide that information.

I'm unsure of whether I've been too light on some topics while too heavy on others. I also feel like a few things are still missing. As always, feedback is appreciated, especially about things you'd like to see written about!
Completed patch searching for rust docs
Made temporary changes to include multiple keywords in rustdoc search

Implemented search based on multiple keywords

Added some commenting and house cleaning

Added path searching to rustdoc