Merge PR #346 (Add KPP-Standalone plotting scripts)

This merge brings PR # (Add scripts to plot vertical profiles
from the KPP-Standalone box model, by @yantosca) into the GCPy
1.6.0 development stream.

This PR adds some scripts to visualize output generated by
the new KPP-Standalone box model (which now ships with
GEOS-Chem 14.5.1 and later versions).

Signed-off-by: Bob Yantosca <yantosca@seas.harvard.edu>

CHANGELOG.md

@@ -10,6 +10,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Added module `benchmark_gcclassic_stats.py` for scraping statistics from GEOS-Chem Classic cloud benchmarks
 - Added dry deposition velocity comparison plots in 1-month cloud benchmarks
 - Added `gcpy/benchmark/modules/benchmark_species_changes.py` to compute the table of species changes between versions
+- Added `gcpy/kpp/` folder containing scripts to plot output from the KPP-Standalone box model
 
 ### Changed
 - Changed format of `% diff` column from `12.3e` to `12.3f` in benchmark timing tables