Replace `failure` with `thiserror`

[ubolonton]

Most improvements from failure are now incorporated into std::error::Error.

• Convenient definition of structured errors is now covered by thiserror. This should be used to defined core error types.
• Quick-and-easy error handling is now covered by anyhow. This is what modules should use.

This is also the chance to drop the Send + Sync requirement on core error types, and therefore the clunky TempValue type.

See also:

• https://www.reddit.com/r/rust/comments/dfs1zk/2019_q4_error_patterns_snafu_vs_errderive_anyhow/
• https://blog.yoshuawuyts.com/error-handling-survey/