create_gas_mix() list

[GraysonBellamy]

🚀 Feature Request

Perhaps we make the input to create_gas_mix() two lists with names and percent compositions respectively.

🔈 Motivation

Eliminates having to have a bunch of different input variables for each gas and composition

🛰 Alternatives

📎 Additional context

[ULibrady]

Gas list is now a dictionary (I thought there would be fewer errors and issues with tracking indexes, but I can change it back)