crab_era computes time relative to the Crab Epoch (the commit of Rust 1.0, a59de37e).

Example:

```rust use chrono::{ DateTime, Utc, };

use crabera::{ crab, tocrab, };

let t3339 = "2022-04-14T23:41:20+00:00"; let ndt = DateTime::parsefromrfc3339 (t3339).unwrap ().naive_utc ();

let c = to_crab (ndt); let roundtripped = crab (c).unwrap ();

asserteq! (c, 218406860); asserteq! (DateTime::::fromutc (roundtripped, Utc).torfc3339 (), t_3339); ```

Made by 🦀 with 🦀 for 🦀 to 🦀