Event-level collection of stats (memory and time collectors for the moment)

* Updated config file with 'events' array element to control enabling, collector selection, and event identifiers
* Switched Options constructor so optional variable ($config) is at the end
* Created new EventListener to handle event collection
* Removed old, unimplemented EventCollector class
* Cleaned up logic in TimeCollector and MemoryCollector to allow for any event to be registered
* Updated time and memory template: scrolling rollovers (lots of events logged by default now); time rollover now has the trigger file and line, and the target class; memory rollover now has the trigger file and line
* CSS formatting and additional items to handle scrolling changes.
* .gitignore now ignores the vendor directory
* Added version to composer.json so we can start doing semantic versioning