renarin_short: function to generate forecast for a given ticker
In DavisWeaver/stonkr_public: Quantitative trading for the people

use nnet forecasting to evaluate future stock price.

renarin_short(
  ticker,
  vendor = "yahoo",
  look_back = 200,
  look_ahead = 14,
  lag = 10,
  decay = 0.2,
  zoom_in = TRUE,
  PI = FALSE
)

`ticker`	security name, e.g. AAPL
`vendor`	provider for data: leave at yahoo unless you have paid for the quandl sharadar equity prices data feed.
`look_back`	number of days to look back for predictions: default is 200
`look_ahead`	number of days to forecast: default is 14
`lag`	number of days to use to fit the next day in the model
`decay`	NNET parametar
`zoom_in`	should function return full model and forecast results? useful for highlighting speicific issues
`PI`	logical: should we compute prediction intervals?: under development