Added information about parent entity to schema (it's located in "parent_entity" entity parameter inside schema), both for Ifc2x3 and Ifc4.
Modified get_entity_doc and get_attribute_doc - now you can use additional optional parameter `recursive=True` with those functions - then parent entities attributes will be included to the list of entity's attributes. For example IfcWindow will also have attributes from IfcBuildingElement, IfcElement, IfcProduct etc...
The schema for IFC4 the same as it was for IFC2x3.
Properties schema for IFC4 includes both quantity and propety sets.
Also cleaned up entities description for IFC2x3 from HTML code and IFC tags.