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.
Ignore tests on Android correctly
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
    }
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
    }
auto merge of #9698 : sanxiyn/rust/android, r=huonw
Correctly report errors for ambiguous default methods
rustdoc: Document what's going on throughout

This addresses some of @huonw's in #9691 about the startling lack of
documentation guiding one throughout the innards of rustdoc::html
Rewrite lint passes with less visitor cruft

This purges about 500 lines of visitor cruft from lint passes. All lints are
handled in a much more sane way at this point. The other huge bonus of this
commit is that there are no more @-boxes in the lint passes, fixing the 500MB
memory regression seen when the lint passes were refactored.

Closes #8589
auto merge of #9686 : alexcrichton/rust/lint, r=thestinger

This purges about 500 lines of visitor cruft from lint passes. All lints are
handled in a much more sane way at this point. The other huge bonus of this
commit is that there are no more @-boxes in the lint passes, fixing the 500MB
memory regression seen when the lint passes were refactored.

Closes #8589
Update std::ops docs as per feedback

from @chris-morgan
auto merge of #9522 : steveklabnik/rust/doc_std_opts, r=alexcrichton

Added an overview with a 'real' example, as well as toy implementations of all of
the traits.

Closes #9356.