use option_env! instead of env!
Pre-step towards issue #12624 and others: Introduce ExprUseVisitor, remove the
moves computation. ExprUseVisitor is a visitor that walks the AST for a
function and calls a delegate to inform it where borrows, copies, and moves
occur.

In this patch, I rewrite the gather_loans visitor to use ExprUseVisitor, but in
future patches, I think we could rewrite regionck, check_loans, and possibly
other passes to use it as well. This would refactor the repeated code between
those places that tries to determine where copies/moves/etc occur.
Convert delegate to use an object type and remove FIXME from closed issue
rustdoc: refactor and unstyle inline section headers
doc: perform some 80-chars wrappings
syntax: `Mod` records the span for inner contents.

this is useful when the module item and module contents are defined
from different files (like rustdoc). in most cases the original span
for the module item would be used; in other cases, the span for
module contents is available separately at the `inner` field.
test: Rename a test to bypass UAC on windows
rustdoc: style tweaks
rustdoc: External module item links to the module contents. Fixes #12926.

the basic strategy is to distinguish `mod foo;` from `mod foo {...}`
by checking if the span for the module item and module contents is
in different files. if it's the case, we prefer module contents.

it is technically possible to fix #12926 without changing the AST,
probably by checking the individual items' span. this is not without
a problem though, since it is possible that some items inside
`mod foo {...}` may have originated from other file (e.g. `include!`).
therefore it is better to record both spans explicitly.
add BigUint subtraction underflow error message
Add a streaming parser to serialize::json.
Fix a code formatting issue in json.rs
Update libworkcache with libserialize's json changes
Fix test issue-4016.rs with the json API change
doc: Remove out-of-place debug! note

As of cc6ec8df, the Owned closures example uses println! instead of
debug!, making a note about seeing debug seem out-of-place in this
section.

Since debug! is not used elsewhere in the tutorial, remove the note
entirely.
auto merge of #13801 : ryantm/rust/master, r=alexcrichton

The previous error message using assert_eq! was quite cryptic. This should be more clear. I also added a test for the underflow case.
std: Rewrite crate docs

Also move prelude explanation to the prelude module.
auto merge of #13809 : prattmic/rust/tutorial_debug, r=alexcrichton

As of cc6ec8df, the Owned closures example uses println! instead of
debug!, making a note about seeing debug seem out-of-place in this
section.

Since debug! is not used elsewhere in the tutorial, remove the note
entirely.
Fix repeated module documentation
test: Fix run-make on windows