Remove colour

[nikolai-b]

I tried running this on my computer but I got an error with:

rast = fasterize::fasterize(overlined_buf_tmp, raster = rast, field = i, fun = "sum")
Error: cannot allocate vector of size 72.6 Gb

I was going to try just changing the raster::RGB(alpha = T) but I couldn't get that far 😢,

When I coloured before I used https://github.com/npct/pct-lsoa-vis/blob/master/tile.sh#L46.

I've no idea if raster::RGB is faster or slower than gdaldem (looks like raster::RGB uses grDevices::col2rgb https://github.com/cran/raster/blob/master/R/RGB.R#L79) but it is nice that we are in R.

We need an alpha channel in the tiles or they overwrite other map features.

[nikolai-b]

One way of solving #4