Init 0.2.2
Merge branch 'master' into V0.2.2
_
Removal of css selector combinator functions.
Separate changelog.
Refactoring

- Moved the parent protocol as an internal protocol of the selectors
namespace
- Merged the basic and combinators selectors into a unique namespace
Moved all the selectors protocols away from the core ones.
Moved away the Tree protocol since it's used only in precompilation.
Moved the visitor  implementation in its own namespace.
Fixed some exentsibility problem.
Cleanup
Refactored simplification.
Refactoring.
More refactoring.
Docstrings and typos.
Cleaning some tests.
Forgotten case.
Updated readme.
Cleaning
Corrections.