PR: https://github.com/litehtml/litehtml/pull/401
This PR implements the scrolling of web pages with fixed elements:

position: fixed

Some changes in API.

The function:

void document_container::get_client_rect(litehtml::position& client) const;

renamed to:

void document_container::get_viewport(litehtml::position& viewport) const;

get_client_rect was a legacy when litehtml was developed for Windows only. Now the name get_client_rect doesn't meet the functionality this function does.

Documentation is in the sources tree now: https://github.com/litehtml/litehtml/blob/master/doc/using.md
Also docs are updated for the latest litehtml.