[new-unit] Energy units

[balporig]

Description

New Energy units

Units to be added

Unit name	Property	Reference to the conversion formula
BTU	Energy	British thermal unit - Wikipedia
kilocalorie	Energy	Calorie - Wikipedia
kilojoule	Energy	Joule - Wikipedia
Watthour	Energy	Kilowatt-hour - Wikipedia

[FrViPofm]

Unit name	Property	Reference to the conversion formula `
toe	Energy	Ton of Oil Equivalent - Wikipedia
Ah / C	Charge capacity	Ampere hour - Wikipedia / Coulomb - Wikipedia