XTCE13 — LinearAdjust -- slope should default to 1

This seems an old issue. Slope is optional and intercept is optional. But intercept defaults to 0. Slope has no default. The generated classes then return a Double and double. Seems like slope=1 by default would be a good thing.

Btw there's a related issue of having this return doubles when they are only being used in non-float number evaluation.