THOR version 2.1.0

A number of bugs have been fixed, including an error in the dynamical core and some minor issues in the diffusion scheme. Python plotting utility has been cleaned up and enhanced to allow users more flexibility, and now includes a "regrid" function that interpolates output properties onto a lat-lon-pressure grid. Benchmark experiments for acoustic wave and gravity wave behavior have been added (based on Tomita & Satoh 2004). Python code (tools/thor_ic_gen.py) has been created that allows the user to "manually" edit initial vertical profile. Differential operators are now output to grid file to facilitate post-processing. The code tools/THORtestrunner.py has been added as an additional benchmarking tool. A crash report tool has been added to assist in the debugging and development process. See changelog.md for additional details.