(std::net::parser): Fix capitalization of IP versions
(std::net::parser): Fix capitalization of IP versions

Also add some missing punctuation in doc and code comments.

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