*** A (SEUCK sprite file format)
*** Document revision: 1.1
*** Last updated: Oct 26, 2017
*** Author: Zoe Blade

Reverse engineering the SEUCK sprite file format (.A files):

The filename is 16 characters long.  The main part is padded with
spaces to 14 characters so that the ".A" suffix is always at the
very end.  For example, "FOO.A" becomes "FOO           .A".

The filename is always entirely uppercase.  Character codes used
are: 65 through to 90 for letters; 48 through to 57 for numbers; and
32 for a space.  Character code 46 is used for the full stop, but
only for the extension separator, not within the main part of the
filename.

The file itself is 8130 bytes long.

The first two bytes are 00110000 00110000.

The remaining 8128 bytes contain 127 sprites (numbered 000 through
to 126 in SEUCK), each 64 bytes long.

Each 3 bytes represent a row of pixels: 12 pairs of bits.  21 rows
make 63 bytes.

Each pair of bits determines the pixel's colour:

00 Background  1
01 General col 2
10 Changeable  4
11 General col 3

The last byte consists of two nibbles: 0001; then the sprite's
changeable colour.

The general colours and transparency colour are not stored in the
file.