redox_users

This release comes with several API changes:

• The most exciting (for me) is the introduction of marker types for AllUsers/User. This allows the compiler to enforce correct usage of the password manipulation API between these two types. This allows many possible panics to be hidden from users of the library and should make the library easier to digest and use correctly.
• User and Group no longer implement FromStr and Display. These had been used to parse/serialize lines from the passwd/group files; however, those were implementation details and should not have been exposed to the user. It's conceivable that these traits would be implemented again in future if a standard input/output format could be agreed upon.
• The Debug implementation for User was fixed.
• Parsing now reports line numbers when failures occur. Invalid lines are also no longer ignored: this has some potential to case breakage, but I expect this to be a small risk.
• I combed the documentation again and utilized the new documentation linking that was recently released.