Error bands example, minor API additions

[Vindaar]

Mainly adds an example on how to create a manual error band plot.

* v0.3.3
- add ~hideLine~ for ~Trace~ object for scatter plots, in order to set
  the line width to 0. Used for backwards compatibility, because
  setting a value of 0 would be the default.
- add ~FillMode~ value of ~toSelf~ to allow colored bands / filled
  polygons
- add example for a manual error band