Merge pull request #5 from zignd/add-is-err-composition

Add IsErrComposition to help check if a custom error type is a composition of Err

Merge pull request #4 from zignd/skip-nil-data-json

Skip nil data from serialized JSON

Merge pull request #2 from zignd/fix-errors-serialization

Fix errors serialization

Add WithCause

Add WithStack and rename Error to Err to allow composition

Refactor the package

- Add support for Go modules
- Add support for Go >= 1.13 errors
- Improve the stack trace serialization
- Rename the "context" for "data" to avoid conflicts with Go
  context.Context
- Add a new example

Fix typo in README.md