in geometry examples, show a move(hkl) & rel_scan near the (440)

[prjemian]

For the (hk0) scan near the (440), do this with a move to (440), then bp.rel_scan(). It's a common type of scan to demonstrate.

Do this for all existing geometry examples (examples/geo_*.ipynb).

[prjemian]

A scan (RE(bp.scan([fourc], fourc.h, 3.9, 4.1, fourc.k, 3.9, 4.1, 5))) already exists at the (440).

Add this new move and rel_scan() after the existing content.

[prjemian]

Also, refactor to use the hkl.geometries.SimMixin() class to replace boilerplate code in the examples.