Responsive Linear Regression Channels

28 sept 2020

This is a linear trend indicator that can:
- automagically adjust to different chart resolutions
- snap to day/session boundaries on intraday
- totally not do the above and use ye olde good fixed lookback window
- show the regression trend and its RMSE channels
- disregard the trend and just show the period average and standard deviation lines (often acting as support and resistance)

The main idea was to allow you to quickly view linear trends for different time periods without having to calculate the required amount of bars.
By default, you will be able to quickly switch between 1-3 months, 6 months, 1 year, 2 years and 5 years of data, as well as various daily lookback periods.
Please adjust resolution settings to your liking.

Caveats:
- More data means more noise and slower calculations.
- HLC3 source is recommended, especially at resolutions above hourly.
- Trend will be slightly different if you use extended hours.
- If you use extended hours and don't have a data subscription, trend will be SUBSTANTIALLY different, especially at smaller resolutions like 1m.
- You might want to use 3.5 days per week for crypto (it's 7 days by default).

Known problems:
- If you can't see the trendlines, scroll to the left or zoom out - the origin could be outside of your viewport.
- Futures' sessions start on the previous day. We currently snap only to day boundaries, not session breaks.
- UVXY and the like that have extremely high price datapoints. The calculations will be wrong on some resolutions.
- Replay can freeze circa bar_index 244 — disable smart lookback and keep your window under 240 bars if you encounter this.

ACKNOWLEDGEMENTS:
Many thanks to alexgrover for his extremely efficient functions (used with permission)