Singapore 1-hour and 3-hour PSI, updated hourly from NEA

Updates are sent when PSI:
- is >100
- is >150, 🔔
- decreases below 100 or 150
- increases by >15/45
- increases by >5/15 if PSI >100, 🔔

https://uu.sg/psi
Send feedback/qns to @zhongfu, tyvm