Hi Przemyslaw
The reference page I use is https://docs.atlassian.com/jira-software/REST/ which gives access to lots of versions of the Jira Software API but stops at 7.3.1.
I guess this might mean that there are no updates to it since then and it is a stable API?
Looking at https://docs.atlassian.com/jira-software/REST/7.3.1/ I can see all the methods previously linked to the Greenhopper API.
Hope this helps although it is not for the version you were looking for but should point you (and others in the future) where to look for the published API pages.
Phill