Angle of Bollinger Bands Alert

This script is used to calculate angle of Bollinger Bands and also setup alerts.

The angle is based on the rules:

- if the previous 2 is 1.1, previous 1 is 1, and the current is 1.1, then the angle should be 90 degrees.
- if the previous 2 is 0.9, previous 1 is 1, and the current is 0.9, then the angle should be 270 degrees

If upper angle is below 90 degrees and close is above the average, it is long signal.
If lower angle is above 270 degrees and close is below the average, it is short signal.

- It is good for catch trend trading.
- Not good for swing trading as the BB changes are very tiny but angles for upper may hit below 90 degrees or angle of lower may be above 270 degrees.