Rename query.entity() and query.get()

[cart]

query.get::<Component>(entity) is now query.get_component::<Component>(entity)

and

query.entity(entity) is now query.get(entity)

This terminology is both clearer and gives the preferred action (getting the full query) precedence. This should be preferred because individual component lookup is slightly more expensive (due to additional safety checks). However for larger queries its probably still cheaper to do an individual component lookup if all you care about is a single component.