explore: Analyse exploration around a central place like a waterhole
In rpatin/PatchExplo: Describing Central Place Exploration

explore compute percentage and total area explored in each distance class around the central place, for each day. It also compute the new area explored at the beginning of the first day. It can work with any sequence of movement, given each sequence as a unique index value

1 2	explore(data, buffer = 100, maxdist = 10000, binsize = 1000, projstring, waterholes)

`data`	a data frame with coordinates `data$x` and `data$y`, and nearest waterhole in column `data$name`. It should be a movement sequence for a single animal and a single exploration event.
`buffer`	width of exploration around the trajectory.
`maxdist`	maximum distance to the central place above which we ignore exploration
`binsize`	width of distance rings
`projstring`	CRS projection of data
`waterholes`	SpatialPointsDataFrame with waterholes location and column `$name` in data slot.