[pshaiCmd] Linear Regression TradingView style (linreg)

Linear Regression calculated the same way as TradingView does, using LR_Intercept and LR_Slope types.

Example/Usage:

local c = ClosePrices()

local linreg1 = CC_LinReg(c, 50, 0)
local linreg2 = CC_LinReg(c, 50, 25)
local linreg3 = CC_LinReg(c, 50, -25)

Plot(0, 'linreg1', linreg1, White)
Plot(0, 'linreg2', linreg2, Orange)
Plot(0, 'linreg3', linreg3, Purple)