[Corona SDK] Support all screens resolution.

config.lua

application =
{
    content =
    {
        scale = "letterBox",
        xAlign = "center",
        yAlign = "center",
        imageSuffix =
        {
            ["-2x"] = 1.5,
            ["-4x"] = 3.0,
        },
    }, 
}

local modelName = system.getInfo( "model" )
local ratio = display.pixelHeight / display.pixelWidth

----------------------------------------------------------------------
-- iOS devices
----------------------------------------------------------------------
if string.sub( modelName, 1, 2 ) == "iP" then
    -- iPad
    if string.sub( modelName, 1, 4 ) == "iPad" then
        application.content.width = 360
        application.content.height = 480
    -- iPhone
    else
        application.content.width = 320
        -- iPhone 5
        if display.pixelHeight > 960 then
            application.content.height = 568
        else
            application.content.height = 480
        end
    end
----------------------------------------------------------------------
-- Android devices
----------------------------------------------------------------------
else
    if display.pixelWidth >= 600 then
        application.content.width = 360
    else
        application.content.width = 320
    end
    application.content.height = application.content.width * ratio
end