Add Non-Templated SystemManager::update() Method

- Added a non-templated updateAll() method to the SystemManager that
updates all systems in the manager.
- Adds a test for updateAll().
Rename SystemManager::update_all() and Add Documentation

- Renamed SystemManager::updateAll() to SystemManager::update_all() to
make it consistent with the existing naming convention.
- Added documentation for SystemManager::update_all().
Merge pull request #76 from excaliburHisSheath/master

Add SystemManager::update_all() Method