Update hd44780.go

[Cruiser79]

Add method CreateChar.
Example code:

bufPlay := []byte{0x0, 0x8, 0xc, 0xe, 0xc, 0x8, 0x0, 0 }
hd.CreateChar(0, bufPlay)
hd.WriteChar(0)

To build custom characters, use https://omerk.github.io/lcdchargen/