* Add 'default' slot option + implicit fills; tests; docs
* Differentiate between standard fillnodes and implicitfillnodes on type lvl
* Reworking slot-fill rendering logic. Simplifying component interfact. Add new get_string_template method
* First working implementation of chainmap instead of stacks for slot resolution
* Stop passing FillNode to Component initalizer -> better decoupling
* Treat fill name and alias and component name as filterexpression, dropping namedvariable
* Name arg of if_filled tags and slots must be string literal
Apply black formatting
Add component_css_dependencies_tag and component_js_dependencies_tag tags
Add convenience methods render_css_dependencies and render_js_dependencies to component class
Create additional test cases
Add license to setup.py
Add pytest.ini config file
