[IMPROVE] Futures Curve Tenor Display

[skhan877]

Two suggested improvements to be made to the futures curve function...

1. The contract shows as a datetime in the --raw table output, which is meaningless in this context. Also the header "Futures" is an odd choice. Perhaps "Last Price" would be better.

futures/curve -t ES --raw

2. The chart visual has a continuous date x-axis. In the context of futures curves, the convention is to show more of a discrete x-axis, corresponding to the actual tenors of the curve.

futures/curve -t ES