Manual: Change `Language items` `sync` to `share`. Fix minor sorting mistake

The *Language item* `no_sync_bound` in [Marker types](http://doc.rust-lang.org/rust.html#marker-types) has been replaced with `no_share_bound`. This updates the manual and does a minor sorting fix.

Fixes https://github.com/rust-lang/rust/issues/16414

cc @cmr 

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