Release 0.6.1 - Xarray interface to implement QGField methods

Major update:

• Thanks Christopher Polster @chpolste for developing an xarray interface for the QGField object using the SOR solver to compute reference state as documented in Nakamura and Huang (2018, Science).
  • Sample code that use this interface: examples/nh2018_science/demo_script_for_nh2018_with_xarray.ipynb
  • Please refer to the corresponding xarray interface documentation page for details.

Minor update:

• Added .gitignore for this repo
• Fix documentation display on readthedocs.io
• Fortran code files are now moved to hn2016_falwa/f90_modules/ such that the compiled .so modules are located in hn2016_falwa/
• Cleaned up f2py modules and remove unused variables

Code change

Detailed change in the code can be viewed on this GitHub commit comparison page:

https://github.com/csyhuang/hn2016_falwa/compare/44fabe7..a656062