Site Finder

[jack-davison]

This PR implements #29.

In short, it adds searchNetwork(), a sister function to networkMap(). Instead of visualising whole networks, it allows users to define a target lat/lng and filter sites based on their distance from the target.

It also adds convertPostcode(), which converts a valid UK postcode to a latitude/longitude pair.

palace <- convertPostcode("SW1A1AA")
searchNetwork(lat = palace$lat, lng = palace$lng, source = c("aurn", "aqe", "local"), max_dist = 20, year = 2020)