godot3 draw_string with BitmapFont

1. building bitmapFont
1. drawing image file(gimp?)
2. make fnt with BMFont
2. editing .fnt ( little hack ?)
1. lineHeight as fontHeight
2. xadvance as fontWidth
3. using in godot3
1. ideas https://github.com/godotengine/godot/issues/15023 

var font = BitmapFont.new()

func _ready():
    font.create_from_fnt("res://fonts/n10.fnt")

func _draw():
    draw_string(font, Vector2(0, 50), "0123456789")