Rephrase some doc items and add API reference links
Rephrase some doc items and add API reference links

SpineEventEngine/SpineEventEngine.github.io,SpineEventEngine/SpineEventEngine.github.io,SpineEventEngine/SpineEventEngine.github.io,SpineEventEngine/SpineEventEngine.github.io,SpineEventEngine/SpineEventEngine.github.io,SpineEventEngine/SpineEventEngine.github.io