liburl: rename and move from_str to Url::parse_str.

url::from_str => url::Url::parse_str

The FromStr trait still works, but its confusing to have a from_str
free function that retuns a Result, while the regular from_str
returns an Option, hence the rename.

[breaking-change]
liburl: rename and move path_from_str to Path::parse_str.

url::path_from_str => url::Path::parse_str

The FromStr trait still works, but its confusing to have a path_from_str
free function that retuns a Result, while the regular from_str style
functions return an Option, hence the rename to indicate a Result.

[breaking-change]
liburl: remove redundant fields in Url.

url.path - Now a Path instead of a String.

To fix old code:
url.path => url.path.path
url.query => url.path.query
url.fragment => url.path.fragment

Not much point having the Path struct if it's not going to be used.

[breaking-change]
liburl: Simplify encoding/decoding using iterators.
liburl: Remove some unnecessary allocations.

Some signatures have changed from String to &str returns.

To fix, call to_string() on the returned value.

[breaking-change]
liburl: cosmetic test changes.
liburl: Generic input for {en,de}code.
librustc: Apply null pointer optimization to slices, closures and trait
objects.
librustc: Remove match arm since we don't allow enum to float casts.
rustc: Reorder error and note message to reduce confusion.

Moved note after error to reduce confusion when the pair appears in the
middle of other errors. Closes #13279.
librustc: Don't create &[T] slices with NULL as the ptr.
Add tests for null pointer opt.
Remove entry_bcx from FunctionContext

We no longer need to refer to the entry block from arbitrary places, so
we can drop it from FunctionContext.
librustc: Accept type aliases for structures in structure literals and
structure patterns.

Closes #4508.
move lifetime suggestion note to after the error

Closes #15433.
Update RELEASES.txt

Fix Typos
libcore: Fix Items iterator for zero sized types.
Fix #15453
Improved example in the Guide

Fixes https://github.com/rust-lang/rust/issues/15452
auto merge of #15431 : iliekturtles/rust/13279-error-msg-order, r=pcwalton

Moved note after error to reduce confusion when the pair appears in the
middle of other errors. Closes #13279.