Kayboard layouts are $200 bytes file containing mapping from NKC to ASCII. The
byte index is the NKC and the value at that index is the ASCII value. 0 means
no mapping.

The file is split into 4 $80 byte areas. The first area is for keystrokes
without any modifier key. The following area is for when the Shift key is
pressed. Then comes RAlt (often called "AltGr"). Then Shift + RAlt.

For example, byte at index $c1 of the "us" layout is 'A', which is the ASCII
mapped to NKC $41 with the Shift key held.

Layouts:

us  US Layout
dk  Danish Layout
dv  US Dvorak Layout
