ffi/c_str.rs: Make all descriptions have a single-sentence summary at the beginning
ffi/c_str.rs: Make all descriptions have a single-sentence summary at the beginning

Per https://github.com/rust-lang/rust/pull/44855#discussion_r144048837
and subsequent ones.

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