[Tile-serving] Configuration files for osm2pgsql

[Andy Allan]

Hi All,

The latest release of osm2pgsql (0.84.0) has a style.lua file, along
with the default.style. I understand that the lua file is (currently?)
optional, and repeats what is implemented in the C code.

The lua file contains polygon_keys and generic_keys but it's not clear
to me how they interact with the default.style.

Does the style.lua file make the default.style redundant? Or do you
need to keep them in sync if you're using the lua rules? The example
in README_lua.md suggests that you need both.

Cheers,
Andy