Inflation-adjusted performance

OVERVIEW
The Inflation-adjusted performance indicator plots an adjusted closing price for the asset
on the main chart by multiplying the asset price by an inflation factor which is derived from CPI-U. The indicator has a `lookback` length, which is used to lookup the CPI-U index value from `lookback` years ago.

The inflation adjusted price is then calculated as `inflationAdjustedPrice = CPIToday / CPIBackThen * currentPrice`

CONCEPTS
This can be a useful tool to assess how an asset has performed as a store of value and inflation hedge over a given period.

The following are the key concepts and user inputs for the oscillator:

• Input: The user can specify the lookback period, in years, using the `lookback` attribute on the settings widget. Defult is 13.
  
• CPI Data: The indicator uses CPI data from tradingview's BLS feed.
  
• Inflation Factor: An inflation factor is calculated by dividing today's CPI by the CPI from the lookback period. This factor represents the increase in prices due to inflation over the lookback period.
  
• Inflation-adjusted Price: The offer price of the asset from `lookback` years ago is adjusted for inflation using the calculated inflation factor. This adjusted price represents what the offer price would be today if it had kept up with inflation.