Release 1.3.0

Issue to release 1.3: #116

Major changes

Major changes 1, 2 and 4 below lead to small changes in output values of QGField compared to the previous release. Users may compare the plots on example jupyter notebooks over different releases to gauge the magnitude of difference.

1. User can put in already interpolated (on evenly-spaced vertical grid) fields from hybrid coordinate interpolation by setting data_on_evenly_spaced_pseudoheight_grid=True to avoid interpolating twice - vertical interpolation is delegated to scipy instead of fortran modules. The old interpolation f2py modules is renamed compute_qgpv (as this is its sole duty now). (See #94 for the discussion.)
2. Compute Static Stability in original vertical coordinates (before vertical interpolation) with UnivariateSpline and its derivative to reduce the numerical error, leading to a smoother field
3. The behavior of QGField.compute_reference_state is modified such that even when Uref cannot be computed, users won't get an error and can still access Qref computed. A boolean parameter QGField.nonconvergent_uref is added to indicate whether Uref is properly computed. If False, compute_lwa_and_barotropic_fluxes cannot be called.
4. Added QGField.compute_lwa_only to provide users with a choice of computing solely LWA from Qref. That way, even if Uref cannot be solved for purely numerical reason, LWA can still be calculated from Qref. This method is available in QGDataset too.

Additional utilities

1. Added "Plot Utilities" (for plots presented in POD contribution to MDTF), "Statistics Utilities" (to compute covariance between <LWA> and <U>) and "netCDF Utilities"
2. Added "Preprocessing" module which include gridfill function used in MDTF with documentation
3. Included developers/run_through_notebooks.sh to run through notebooks for each release

Minor fixes

• Fixed the build test in Git Workflow
• Fixed Sphinx build on ReadTheDoc
• Fixed misformed link in documentation