Closes #3

[HughParsonage]

Function now accepts latlon argument, returning current_weather of nearest station (in the internal table) with a message. Uses haversine_distance (as internal function) to calculate the distance to avoid dependencies on packages. Slightly less accurate but fine for this purpose.

Outstanding issues that are not in scope for this PR:

• Not all stations have their latitude-longitude recorded. This is a limitation of the BOM's API which uses inconsistent names across various outlets.
• Nonstandard weather stations (oceanic buoys).
• Internal table names() may need to be rethought.

[HughParsonage]

I believe the patch diff failure spurious. Subsequent commit reduced total lines, even though coverage has increased. Coverage miss in current_weather is only achieved if the server is down (i.e. can't be reproduced).

[adamhsparks]

Thanks @HughParsonage

Merged.