Support scraping heats/events from a competition

[zeskeertwee]

From #12, support scraping https://www.athletics.app/wedstrijd/uitslagenonderdeel/[competition ID]/[event]/, where event is e.g. 100m 100m_hf etc. Example: https://www.athletics.app/wedstrijd/uitslagenonderdeel/41655/100m_f/