Improvements for the main package vignette

[ajaynshah]

1. It would be better if the identical ylim were used for Figure 1 and Figure 2, so that the variance reduction is visually apparent.

2. A little more work on interpreting Figure 3 would be useful. I think I see the market revving up the stock price from about -20 minutes on.

3. We require a package that will work with all possible time frequencies (intra-day, daily, weekly, monthly, quarterly, annual, non-specific integer valued time). And, the package vignette needs to flaunt this so that it does not look like a stock market + AMM story alone.