improve some naming in Event::IcalRenderer.
extract more private methods out of Event::IcalRenderer#add_event.
move entry to an argument in Event::IcalRenderer
metaprogram to remove duplication in Event::IcalRenderer.
refactor Event::IcalRenderer class level methods.
split up Event::IcalRenderer#description.
move Event#multiday? to Event::IcalRenderer since its only used there.
Merge pull request #197 from botandrose/refactor_ical_renderer

Refactor Event::IcalRenderer