Integrate @elextr ['s explanation](https://github.com/geany/geany/issues/1475#issuecomment-296629551) of ABI/API into the `HACKING` document. Resolves #1475. You can view, comment on, or merge this pull request online at:
https://github.com/geany/geany/pull/3027
-- Commit Summary --
* Expand ABI/API explanation in HACKING
-- File Changes --
M HACKING (18) A po/.intltool-merge-cache.lock (0)
-- Patch Links --
https://github.com/geany/geany/pull/3027.patch https://github.com/geany/geany/pull/3027.diff