Elastic Volume Weighted Moving Average & Envelope [LazyBear]

Elastic Volume Weighted Moving Average (eVWMA) is a statistical measure using the volume to define the period of the moving average. The eVWMA can be looked at as an approximation to the average price paid per share. Multiplier is usually the number of shares, but it can be approximated using cumulative sum of volume (Enable it via "Use Cumulative Volume" option) or sum of volume over "n" periods.

I have also added an option to draw eVWMA envelope (eVWMA on HLC).

More info:
christian-fries.de/evwma/PDF/evwma_intro.pdf

List of all my indicators:
- Chart: tradingview.com/v/4IneGo8h/
- GDoc: docs.google.com/document/d/15AGCufJZ8CIUvwFJ9W-IKns88gkWOKBCvByMEvm5MLo/edit?usp=sharing