Falwa

- Great thanks to chpolste for pull request 36 that optimizes the fortran code that computes LWA and fluxes. To incorporate the changes made, after pulling the changes, please re-compile the f2py modules. One way of doing this is:

$ python setup.py develop -u
$ git pull
$ python setup.py develop

- The module `hn2016_falwa/download_data.py`, which downloads ERA-Interim data, has been removed.
- The module `hn2016_falwa/beta_version.py` has been moved to the `legacy/` folder. This module is no longer maintained, and will be deprecated in the upcoming release.
- Added one unit test for the class `BarotropicField`.
- Instead of using Travis CI, now deployment test and code coverage test are implemented using *GitHub workflow*.

close 37

There are two fixes in this release:
- The bugs in the class BarotropicField is fixed. Thanks chpolste for the pull request.
- Now `QGField` can handle masked arrays without raising an error. It converts masked array to numpy array with the `fill_value` stored in the masked array.

Enhancement in functionality
- The computation of LWA, reference state and vertically averaged fluxes in the **Southern Hemisphere** is now available in the `QGField` class!
- The computed variables can be accessed via the QGField class without calling any methods, e.g. the 3D wave activity can be retrieved from the QGField object `qgfield` by `qgfield.lwa`. See documentation/example for all the attributes.
- Added more sanity checks for the inputs of `QGField`.

Other changes
- The documentation page is fixed and now available at [http://csyhuang.github.io/hn2016_falwa](http://csyhuang.github.io/hn2016_falwa).
- Added test data and increase unit test coverage for `QGField`.

- Fixed a bug in the interpolation procedure when the input latitude grid is of even number of points
- Updated the notes regarding the equation solver for the reference state (in `notes/`)

- Replaced `unittest` with `pytest` for more flexibility in testing
- Improved the encapsulation of variables in the module `oopinterface`, e.g. methods like `qgfield.get_lwa()` are replaced by `qgfield.lwa`.

- Enhanced functionality of the class QGField to process latitude grids with even number of grid points.
- Enhanced interface of QGField with some functions to retrieve computed quantities at intermediate steps. See documentation of QGField for details.