Add styling flexibility, "no events" message

Added parameter "includecss" to use supplied style sheet
Added parameter "noeventtext" to display if no events are found
Style sheet inclusion is now conditional, and properly injects it into
the <head> element.
Added detection for number of events to render.
Removed <br /> formatting.
Added CSS classes to <li>, <a>, and new <div> containers for more
flexible formatting.