Remove the core::bool module

[brson]

This module is soon to be used for nothing more than displaying documentation for primitives. As such, it should not exist, but we need somewhere to put the primitive docs, so rustdoc may need some tweaks.

[frewsxcv]

libcore/bool.rs was renamed to libstd/bool.rs in this pull request

[alexcrichton]

This was done!