Excluded files from stable_0.8 from git

Details:

* The .gitignore list was thinned out in recent updates, and this change
  adds back in some files and directories that are created (and to be ignored)
  when switching back to the stable_0.8 branch. So this change better allows
  using the same repo for work on both master and stable_0.8.

Signed-off-by: Andreas Maier <maiera@de.ibm.com>

.gitignore

@@ -20,3 +20,6 @@ tmp_*
 /dist/
 /docs_linkcheck/
 /tests/output/
+/AUTHORS
+/ChangeLog
+/build/