Correlation set update

* overrides.conf: Latest source data corrections from
script-assisted research.

These remaining files are generated data. Normally they're not
something I feel good about committing into version control, but in
this case it allows for logging and tracking deltas in the data over
time...

* airports: Removed 18 airports corresponding to nonexistent
stations.

* stations: Removed 326 stations with no recent conditions, added
429.

* zones: Removed 45 zones with no recent forecasts, added 104.

* places, zctas: Based on latest Census Bureau data corrections,
updated with new correlations.

* overrides.log: Record of correlation set build.

* slist, zlist: State of active stations and weather zones at the
time of generation.