Fixed some broken notification. Introduced bug where observers are never unobserved.
Revert "Fixed some broken notification. Introduced bug where observers are never unobserved."

This reverts commit 4429e3851ea33a13ace5ac5d1f2602f0d9ae1bd7.
Improved clarity and robustness of unobserve method. Removed 'handler' variables and documentation in favor of observer/subject vocab.