Changes to energy units and offset do not affect .calc.energy

[prjemian]

fixes #86

Changes to units or offset will only change .energy, not .calc.energy. To change .calc.energy, must set .energy.

To change energy, offset, & units, do it in this order:

1. set units
2. set offset
3. set energy

[prjemian]

@mrakitin ready for review

[mrakitin]

There is a conflicting file here. Will review once it's resolved.

[prjemian]

@mrakitin Merge conflict is resolved. Ready to review.

[mrakitin]

Looks good! Have a minor, non-blocking suggestion.

[prjemian]

Synchronize instructions to set the energy with #101 (comment) before merging.