PX4 Fixed Wing Mission Acceptance Radius

NPFG is the replacement for the Fixed Wing L1 navigation in PX4 v1.14. I’m still waiting for a bit of explanation on how it differs and what docs we need (though we fixed up the parameters in various places in the docs). I am GUESSING it stands for Nonlinear Path Following Guidance or similar, but who knows. Perhaps @tstastny or @sfuhrer could answer that too.