PR for Review Round 2

[coroa]

Fixes #32 , #34 and #36 .

• [x] Data type is used from proxy (and indexraster)
• [x] Check and correct dimension order:
  • [x] aircraft: time, level, lat, lon
  • [x] anthro: time, sector, lat, lon
  • [x] openburning: time, sector, lat, lon
• [x] Sectors are not dropped by empty proxy weights (restores Agriculture and Solvents in BC)
• [x] Sector order in proxies is preserved
• [x] Proxies need to be updated:
  • [x] Sector order in anthro_*-proxies should be 'AGR', 'ENE', 'IND', 'TRA', 'RCO', 'SLV', 'WST' (currently it is alphabetical with TRA in between SLV and WST)
  • [x] Sector order in openburning is fine
  • [x] Data type should be float32 (.astype("float32"))
  • [x] anthro
  • [x] openburning
  • [x] aircraft
  • [x] shipping
  • [x] cdr_co2
• [x] Sector attribute id is called ids instead
• [x] Indexraster needs to use the float32 datatype as well (or we add a quick conversion to workflow.ipynb)
• [x] Agriculture CO2 needs to be added as 0 (still missing because it does not have a variable correspondence in variabledefs)
• [x] Move CO2_em_removal into CO2_em_anthro with documentation
• [x] Add 2015 year to gridded data by stitching historical and downscaled tabular data
• ~[ ] time_bnds between two years are incorrect~ for review round 3
• ~[ ] Check there are no nan's in any of the datasets~ systematic check for review round 3
• [x] Compare to previous set of gridded files (per sector/gas spot checks and grid cell total systematically)
• [x] Add a CHANGELOG

[coroa]

@gidden Ok, with the addition of the changelog the review round-2 work would be complete!