Merge pull request #215 from fizzix/fizzix_merge

Merge fizzix's gameplay changes
Fix up merge - set_recall() started having a return valiue.
Add up-to-date changes file.
Reduce drop frequency for town books as monster drops
(cherry picked from commit 2fe64775ed7ae0a40358e1475f31719756e8ba0c)
Drop object frequencies for all spell books
(cherry picked from commit a310ea72615587ee0fd4c983ef8522133f1a289c)