Document std::ops.

Added an overview with a 'real' example, as well as toy implementations of all of
the traits.

Closes #9356.
std: Replace num::IntConvertible with {To,From}Primitive
syntax: Add #[deriving(FromPrimitive)] syntax extension

Right now this only works for c-style enums.
syntax: swap from .span_fatal to .span_err in #[deriving(FromPrimitive)]
test: add compile-fail test for #[deriving(FromPrimitive)]
std: Swap {To,From}Primitive to use the 64bit as the unimplemented version

One downside with this current implementation is that since BigInt's
default is now 64 bit, we can convert larger BigInt's to a primitive,
however the current implementation on 32 bit architectures does not
take advantage of this fact.
extra: Add ToBigInt and ToBigUint traits
Package system runtime dependencies into snapshots
Package system runtime dependencies into Windows distribution.
Highlight line numbers of the lines referred to in the url hash
Prevent source view from wrapping lines
Make source links highlight the entire definition and not just the first line
rustdoc: Generate hyperlinks between crates

The general idea of hyperlinking between crates is that it should require as
little configuration as possible, if any at all. In this vein, there are two
separate ways to generate hyperlinks between crates:

1. When you're generating documentation for a crate 'foo' into folder 'doc',
   then if foo's external crate dependencies already have documented in the
   folder 'doc', then hyperlinks will be generated. This will work because all
   documentation is in the same folder, allowing links to work seamlessly both
   on the web and on the local filesystem browser.

   The rationale for this use case is a package with multiple libraries/crates
   that all want to link to one another, and you don't want to have to deal with
   going to the web. In theory this could be extended to have a RUST_PATH-style
   searching situtation, but I'm not sure that it would work seamlessly on the
   web as it does on the local filesystem, so I'm not attempting to explore this
   case in this pull request. I believe to fully realize this potential rustdoc
   would have to be acting as a server instead of a static site generator.

2. One of foo's external dependencies has a #[doc(html_root_url = "...")]
   attribute. This means that all hyperlinks to the dependency will be rooted at
   this url.

   This use case encompasses all packages using libstd/libextra. These two
   crates now have this attribute encoded (currently at the /doc/master url) and
   will be read by anything which has a dependency on libstd/libextra. This
   should also work for arbitrary crates in the wild that have online
   documentation. I don't like how the version is hard-wired into the url, but I
   think that this may be a case-by-case thing which doesn't end up being too
   bad in the long run.

Closes #9539
Ignore tests on Android correctly
Close out #9155

Add a test to make sure it works and switch a private struct over to a
newtype.

Closes #9155
auto merge of #9691 : alexcrichton/rust/rustdoc, r=cmr

This slurps in the commits from #9684 as well as closing #9539.
make unit structs immediate

    struct Foo;
    fn foo() -> Foo { Foo }

Before:

    ; Function Attrs: nounwind readnone uwtable
    define void @_ZN3foo18he8ca29755dedebbaf4v0.0E(%struct.Foo* noalias nocapture sret, { i64, %tydesc*, i8*, i8*, i8 }* nocapture) #0 {
    "function top level":
      ret void
    }

After:

    ; Function Attrs: nounwind readnone uwtable
    define %struct.Foo @_ZN3foo18he8ca29755dedebbaf4v0.0E({ i64, %tydesc*, i8*, i8*, i8 }* nocapture readnone) #0 {
    "function top level":
      ret %struct.Foo undef
    }
make C-like enums immediate

This fixes two existing bugs along the way:

* The `transmute` intrinsic did not correctly handle casts of immediate
  aggregates like newtype structs and tuples.
* The code for calling foreign functions used the wrong type to create
  an `alloca` temporary

    enum Foo { A, B }
    fn foo() -> Foo { A }

Before:

    ; Function Attrs: nounwind uwtable
    define void @_ZN3foo18hbedc642d5d9cf5aag4v0.0E(%enum.Foo* noalias nocapture sret, { i64, %tydesc*, i8*, i8*, i8 }* nocapture readnone) #0 {
    "function top level":
      %2 = getelementptr inbounds %enum.Foo* %0, i64 0, i32 0
      store i64 0, i64* %2, align 8
      ret void
    }

After:

    ; Function Attrs: nounwind readnone uwtable
    define %enum.Foo @_ZN3foo18hbedc642d5d9cf5aag4v0.0E({ i64, %tydesc*, i8*, i8*, i8 }* nocapture readnone) #0 {
    "function top level":
      ret %enum.Foo zeroinitializer
    }
Merge pull request #9697 from sfackler/issue_9155

Close out #9155
auto merge of #9699 : thestinger/rust/immediate, r=huonw,luqmana

    struct Foo;
    fn foo() -> Foo { Foo }

Before:

    ; Function Attrs: nounwind readnone uwtable
    define void @_ZN3foo18he8ca29755dedebbaf4v0.0E(%struct.Foo* noalias nocapture sret, { i64, %tydesc*, i8*, i8*, i8 }* nocapture) #0 {
    "function top level":
      ret void
    }

After:

    ; Function Attrs: nounwind readnone uwtable
    define %struct.Foo @_ZN3foo18he8ca29755dedebbaf4v0.0E({ i64, %tydesc*, i8*, i8*, i8 }* nocapture readnone) #0 {
    "function top level":
      ret %struct.Foo undef
    }