Compatibility and performance updates

Added ability to disable browser's default autocomplete mechanism.

changed "mouseup" call to "mousedown" on suggestion <li> elements as "mouseup" is not well supported.

changed "keydown" listener "if" statement to "switch" statement.  easier to read and faster.

modified "focus" listener to accept additional parameter.  previously when a value was selected from the suggestion list, an unnecessary additional event was called due to ".focus()" being called after value was set.

Modified markup very slightly.