* Closes #8: Handling of optional values (#17)
* Refs #8: add optional and required fields to config node
* Refs #8: provide builder methods for optional and required access
* Refs #8: update readme
* Refs #8: Version to 1.1.1
* Fix badge link in readme
* Closes #19: Validation of optional fields throws errors when the field does not exist (#20)
* Refs #19: add tests
* Refs #19: skip None values in validation
* increment version
* Remove accidentally added dir (#21)
* Closes #24: Use proper python 3.7 for travis and cache pip dependencies (#27)
* Closes #25: Add new keys to the config (#28)
* Refs #25: add tests
* Refs #25: implement adding of new elements and add upsert flag
* update readme
* Refs #25: refactor output
* Closes #26: Merge with ENV variables (#29)
* Add documentation to config builder
* Refs #26: add test
* Refs #26: merge environment variables with config
* increment version to 1.1.3
* update readme
* Closes #34, closes #33: Enable config iterations and add to dict method (#36)
* reorganize config node tests
* Refs #34: add iteration functions
* Refs #34: add tests
* organize method order in config node
* Refs #34: add to dict method
* Refs #34: add to dict test
* Closes #32: Revise ENV merging (#37)
* Refs #32: move env merging to config node but keep builder method
* Refs #32: add and update tests
* Refs #32: update readme
* remove unused import
* change comment
* Closes #35: Switch to pytest and add flake 8 linting (#38)
* Refs #35: update readme and add flake8 and pytest
* Refs #35: add pytest ini
* Refs #35: add flake8 and update travis build
* Refs #35: fix linter errors
* Refs #35: remove init file contents
* Refs #35: change tests to pytest
* Version 1.1.4 (#39)
* Closes #23: Serialization methods (JSON) (#41)
* use double quotes wherever possible
* Refs #23: add json serialization
* Refs #23: add test
* Closes #30: Use msgpack for binary serialization (#42)
* Refs #30: add msgpack dependency
* Refs #30: add msgpack serialization and handle unserializable values
* Refs #30: add tests
* Refs #30: increment version
* Refs #30: add msgpack serialization and equality
* Refs #30: add msgpack tests
* Refs #30: add equality test
* Refs #30: update readme
* Refs #30: refactor
* Refs #30: config builder can also parse json strings
* Fixes #46: When upserting a new value in a new subfield, the subfield is not added (#47)
* Refs #46: add test cases for nested update and upsert
* Refs #46: fixes nested upsert and update
* Fixes #45: Environment variable prefix matching (#48)
* Test proper effect in config builder env merge
* Refs #45: add test case
* Refs #45: fix prefix matching
* increment version
* fix linter
* Closes #52: Handle environment variables that overwrite config values with underscores in their names (#53)
* Refs #52: add test for special case
* Refs #52: add method for parsing environment variable names
* Refs #52: use parse method in merge with env variables method
* Fixes #51: Properly set required/optional access in Config Nodes that are created at a later point in time (e.g. upsert) (#54)
* Refs #51: add (failing) test
* Refs #51: correctly pass access options to children added in upserts
* increment version
* Update Readme (#56)
