expect_macro: macro to replace expect/unwrap

This macro allows you to write expect!(my_result) or expect!(my_result, "error: {}", my_result)

See the library docs for more information

LICENSE

The source code in this repository is Licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or
  http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or
  http://opensource.org/licenses/MIT)

at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.