text: Title: Create Standard Deviation for Linear Regression
  Body: I needed to have standard deviation for linear regression and there was not function for it. so i coded it and if you like you can edit it and add to next version.
  
  ```python
  def stdevlinreg(close, length: int):
      x_value = close
      stdev = close
      slope = ta.linreg(close=close, length=length, slope=True)
      tsf = ta.linreg(close=close, length=length, tsf=True)
      variance = 0
      for i in range(1, length):
          variance += (x_value.shift(i) - (tsf - i * slope)) ** 2
      stdev = (variance / (length - 1)) ** 0.5
      return stdev
  ```
  
  so we can now use it as:
  `df['stdlinreg'] = stdevlinreg(df['close'], length=15)
  `
  and if add to 'linreg' it can be like:
  `df['stdlinreg'] = ta.linreg(df['close'], length=15, stdev=True)`