CRL loader
==========
Info by Fabrizio Gennari <fabrizio.ge@tiscalinet.it>

Used by Nato Assault Course, Oink, Pilgrim, Tau Ceti, Time Fighter, Traxxion

Sync: 5 pulses between $600 and $E00 clock cycles, followed by 5 pulses between
$300 and $700 clock cycles.

Threshold: $200 clock cycles
Endianness: LSbF

After sync, data bytes, always a multiple of 256. No checksums.

Structure:
the start address and length (in units of 256 bytes) of first chunk are
hard-coded in header chunk (Kernal loader).

First chunk contains the loader routine, and the code that invokes it (and also
displays/hides loading screen between chunks)

The start addresses and lengths of all following chunks are hard-coded in the
first chunk.

Code in first chunk stores in $04 length (in unit of 256 bytes) of each chunk,
modifies the loader routine with the start address, then does JSR to the loader
routine. It does so for each of the following chunks, until loading is complete.