Possibly change interface

[sckott]

via r-spatial/sf#12

e.g., do

list(Point = c(116.4, 52.2))

instead of the current

list('type' = 'Point', 'coordinates' = c(116.4, 45.2))

it's still early days in the pkg, so not too bad to change if that's a better UI

[sckott]

it might make most sense to accept either format, with or without type as an element in the list. and bonus b/c that doesn't break the package API