Adding oxidised methane to carbon pools

[FrankErrickson]

@kar5469 and I are working on a project that couples in a new methane cycle model into FAIR (but coded up in Julia) and had a quick question on how you handle oxidised methane. It looks like the oxidised_CH4 term is being added to all four carbon pools (i.e. see Line 636 in forward.py).

We weren't sure if we were just misinterpreting something, or if this is actually adding 4x the oxidised CH4 amount? We'd appreciate any thoughts/insights you have.

[chrisroadmap]

Yep this looks like an error - I'll make a PR

[chrisroadmap]

Interestingly this doesn't fail any of the pre-calculated tests: so while it was implemented clunkily it wasn't affecting the model results.