Pre-release 0.6: tests coverage, analyzer, documentation improvements.

- add pytest-cov and ensure 100% test coverage
- make sure the tests cover all cryptographic exceptions
- create test data for all cryptographic issues
- split documentation into multiple pages
- keep reader key associated with DEK
- analyze header packets and data blocks (including DEK index)

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "oarepo_c4gh"
-version = "0.5"
+version = "0.6"
 authors = [
   { name = "Dominik Pantůček", email = "[email protected]" }
 ]