Implement std::error::Error for ApiError

[BroderickCarlin]

The ApiError currently does not implement the std::error::Error trait, unlike many of the other error types within this crate. This can make errors of the ApiError type less ergonomic to handle within frameworks than may expect generic errors.

Simple 1-line fix to just implement std::error::Error with all default methods, given that ApiError already implements Debug and Display

[64bit]

Thank you for the context in description and PR!