Driver for the Hitachi HD44780U dot matrix LCD controller

- Only 4bit parallel interface supported for now
- Write-only operation (RW pin should be connected to ground or held low)
- 1 or 2 line LCDs supported with 5x8 or 5x10 dot fonts.
- Support for creating custom characters.
Note to self: we need to confirm that `panic!()` doesn't bloat.