Update to PyGeodesy 21.8.21

[fraxker]

Back in April, we received this email

FYI,

In PyGeodesy version 21.4.12 the Python class EcefCartesian has been deprecated (and moved to the deprecated module). The very same functionality in now available from class LocalCartesian (in new module ltp).

In your suas-helmsman project, please use

try:
    from pygeodesy.ecef import EcefCartesian
except ImportError:
    from pygeodesy import LocalCartesian as EcefCartesian

instead of only

from pygeodesy.ecef import EcefCartesian

My apologies for making that change but EcefCartesian was incorrectly named and not dealing with ECEF but with local cartesian coordinates.