Pypendency

New container class method inside Container for the tags api:
python
get_services_identifiers_by_tag_name(self, tag_identifier: str, tag_value: Optional[object] = Tag.UNSET_VALUE) -> Set[str]:

Returns all the services identifiers associated with the specified tag.

New functionality added in Container class.

- callbacks for on_resolved_container: You can add multiple callable functions to the container that will be triggered after the container is resolved.

New container class method:
- add_on_resolved_callback(func: OnContainerResolvedCallable) -> None

New type alias for callables: OnContainerResolvedCallable = Callable[[], None]

Create the public Tags API.
- Add Tag class
- Changes to the Container API:
- `set` now takes an extra, optional argument for the tags: `set(identifier: str, service: object, tags: Optional[Set[Tag]] = None) -> None`
- Tags of a service can be retrieved through the service's identifier: `get_service_tags(service_identifier: str) -> Set[Tag]`
- A set of services can be retrieved through their tags:
- `get_by_tag(tag: Tag) -> Set[object]`
- `get_by_tag_name(tag_identifier: str, tag_value: Optional[object] = Tag.UNSET_VALUE) -> Set[object]`
- Tags can also be specified through `yaml`:

yaml
example.tagged_A:
fqn: 'tests.resources.class_a.A'
args:
- 'example.A'
kwargs:
kw_arg: 'test_param'
b: 'example.B'
tags:
test_tag_identifier: 'test_tag_value'
another_test_tag_identifier: empty evaluates to null
yet_another_tag: 1

Stop support for **Python 3.6** since that version is no longer maintained. 16
Using pypendency on a project that uses Python 3.6 may fail as the `dataclasses` package is no longer installed.

- Improve error traceability when instantiation fails 7
- Add absolute path guards 6
- Change pyloader load by system path 5

- Change pyloader load by system path 5
- Add absolute path guards 6