Add support for all radar moments of the ODIM HDF5 format

[vlouf]

Right now in PYART only some ODIM HDF5 field are read, those defined in pyart.aux_io.odim_h5.py:

ODIM_H5_FIELD_NAMES = {
    'TH': 'total_power',        # uncorrected reflectivity, horizontal
    'TV': 'total_power',        # uncorrected reflectivity, vertical
    'DBZH': 'reflectivity',     # corrected reflectivity, horizontal
    'DBZV': 'reflectivity',     # corrected reflectivity, vertical
    'ZDR': 'differential_reflectivity',     # differential reflectivity
    'RHOHV': 'cross_correlation_ratio',
    'LDR': 'linear_polarization_ratio',
    'PHIDP': 'differential_phase',
    'KDP': 'specific_differential_phase',
    'SQI': 'normalized_coherent_power',
    'SNR': 'signal_to_noise_ratio',
    'VRAD': 'velocity',
    'WRAD': 'spectrum_width',
    'QIND': 'quality_index',
}

An improvement for ODIM HDF5 users would be to support all fields defined by the convention (table 16, page 22): http://eumetnet.eu/wp-content/uploads/2017/01/OPERA_hdf_description_2014.pdf

[zssherman]

xradar has an odim reader which should have all the fields for the odim dataset. With the eventually switch to xradar, I think we can close this for now.