Release v0.3.0 - `pam_sys` dependency upgraded, making API changes neccessary - API change: `ReturnCode` replaced by `ErrorCode` - API change: `Flag` now uses `bitflags!` - Support for Linux-specific `PAM_RADIO_TYPE` and `PAM_BINARY_PROMPT` - Optional `serde` serialization support for some types - Added `EnvList -> HashMap` conversion - New `ErrorWith<T>::into_without_payload()` convenience method - Increased test coverage