Improve interpretation of EPA CEMS data during HIFLD grid-building

# :rocket:

- [ ] Is your feature request essential for your project?

### Describe the workflow you want to enable
During HIFLD grid-building, we use EPA's CEMS data to estimate heat rate curves for fossil generators. However, this dataset is known to be noisy. We perform some sanity-check validation on the output of our curve sitting, but it would be nice to be able to include some of the input-side data cleanup and interpretation functions (especially as they relate to combined cycle plant operation) from NREL's National Thermal Generation Performance Database project.
- Paper: https://pubs.acs.org/doi/abs/10.1021/acs.est.9b04522
- Github repo: https://github.com/nrel/NaTGenPD