binary data

[SymbolixAU]

each to_geojson() function could have an equivalent to_binary(), which creates a 'binary' representation of the data so it can use the binaryData prop

https://github.com/uber/deck.gl/blob/master/docs/developer-guide/performance.md#on-using-binary-data

[SymbolixAU]

Now with sfheaders converting to data.frames and keeping properties, I only need one function which works on data.frames.

So the logic is

1. If required, convert sf to data.frame sfheaders::df::sf_to_df( sf, ..., keep = T )
2. process arguments, columns, colours as per normal
3. convert to json by-column jsonify::api::to_json( lst, by = "column" )
4. done.

[dcooley]

now doing in #52