Recent updates

GCAM v5.4:

Several changes have been made to GCAM since the last release version (v5.3). The key updates are:

1. Updated technology costs for electricity and transportation technologies
2. Emissions: using CEDS as data source, updated to 2015, new MAC curves
3. Trade: improved trade for fossil fuels, forestry, and agriculture
4. Included water markets in GCAM-USA
5. Energy for water
6. New food demand representation
7. Solver improvements and library changes
8. gcamdata updated to use drake and work with dplyr 1.0.0
9. Removed unused code
10. Minor updates and bugfixes
11. Optional features (not turned on by default):
    - Direct Air Capture
    - Ability to specify exogenous floorspace pathways
    - Ability to scale CH₄ and N₂O emissions to EPA inventories