Calculations for Southern Hemisphere available now!

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.
• Added test data and increase unit test coverage for QGField.