Added optional userId and customData support for rewarded AD

[blendjam]

This currently supports android devices only. Any help from moderators is welcomed.

[britzl]

Looks good.

This currently supports android devices only

iOS documentation: https://developers.google.com/admob/ios/rewarded#validate-ssv

[blendjam]

Adding support for userId is breaking as load_rewarded expects userId to be passed as argument.

[britzl]

Adding support for userId is breaking as load_rewarded expects userId to be passed as argument.

You're right. It would be better to either have userId and customData as optional extra arguments or provide them in an options table:

local options = {
    user_id = "user_id",
    custom_data = "my custom data",
}
admob.show_rewarded("unit_id", options)

The below change should be enough to treat the values as optional:

static int Lua_LoadRewarded(lua_State* L)
{
    DM_LUA_STACK_CHECK(L, 0);
    if (lua_type(L, 1) != LUA_TSTRING) {
        return DM_LUA_ERROR("Expected string, got %s. Wrong type for Rewarded UnitId variable '%s'.", luaL_typename(L, 1), lua_tostring(L, 1));
    }
    const char* unitId_lua = luaL_checkstring(L, 1);

    char* userId_lua = 0;
    if (lua_gettop(L) > 1)
    {
        userId_lua =  luaL_checkstring(L, 2);
    }

    char* customData_lua = 0;
    if (lua_gettop(L) > 2)
    {
        customData_lua = luaL_checkstring(L, 3);
    }

    LoadRewarded(unitId_lua, userId_lua, customData_lua);
    return 0;
}