Make some adjustments to the documentation for `std::convert::identity`
Make some adjustments to the documentation for `std::convert::identity`

Fixes some extra blank lines and makes some minor tweaks to the wording.

graydon/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust