cartopy: Adding Andrew Dawson as a core developer of cartopy

I’m very pleased to announce Andrew Dawson as a new core developer on the cartopy project. As well as making significant contributions to many
of the fundamental components of cartopy, he has taken the time to extend documentation, review other PRs and help users with issues raised
on github. Of particular note is Andrew’s work on the reprojecting, resampling, and visualisation of vector quantities which is providing a step change in current cartopy capabilities and will inevitably feed through into richer and more diverse scientific analyses for many scientists.

Welcome aboard Andrew!