834 (Benefit Enrollment and Maintenance) about x12-types HOT 2 CLOSED

I put together some very basic support for 834. I recently shifted the parser implementation to nom because the previous approach did not work with more complex EDIs. Sadly I still have no idea how stable the current implementation is. So all of this is still a learning-by-doing (so no contribution guide whatsoever).
I think most errors will appear when this library is used with real data. I also added some test cases, but this only covers a very minimal feature set.
https://github.com/apimeister/x12-types/blob/main/src/v005010/test_834.rs

from x12-types.

implemented display-trait support, as well as macro macro-based parser. So implementation is now on par with the other standards.

from x12-types.