Corrections to geostrophic winds and advective tendencies at (very) high levels

[sjboeing]

No description provided.

[sjboeing]

Working on this in #197, but would be good to follow the general structure of #198. Some examples of valid and invalid files.

VALID_YAML_EXAMPLES = [
    """
wind_at_high_levels_correction_method: "fixed_pressure"
wind_at_high_levels_correction_highest_pressure: 500
wind_at_high_levels_correction_transition_thickness: 200
wind_at_high_levels_correction_shape="cos",
""",
    """
wind_at_high_levels_correction_method: "off"
""",
    """
""",
]

INVALID_YAML_EXAMPLES = [
    """
wind_at_high_levels_correction_method: "off"
wind_at_high_levels_correction_highest_pressure: 500
wind_at_high_levels_correction_transition_thickness: 200
wind_at_high_levels_correction_shape="cos",
""",
    """
wind_at_high_levels_correction_method: "fixed_pressure"
wind_at_high_levels_correction_highest_pressure: 500
wind_at_high_levels_correction_transition_thickness: 200
""",
]

Note an empty example is valid, and should generate sensible defaults. Not sure if the "cos" shape needs to be specified (as the second INVALID example shows) or can be left out.