Datafile descriptions

Document every game data file: name, structures, layout. Each structure that can exist in a file should define total size in bytes. Also declare functions for reading/writing from/to stdio streams, if necessary.

 * File: SEQ.KEY, FSEQ.KEY
 * Desc: Names of movie & audio files, each name 8 bytes long.
 *       Successful mission video sequences are stored in SEQ,
 *       failures in FSEQ.
 * Structure:
 *      u16 - number of subsequent filenames
 *      u8[8]* - filenames, each should be 0 terminated
 * 

 * File: SEQ.DAT
 * Desc: Indexes to video and audio files for successful mission stages.
 * Structure:
 *       sequence of oGROUP structures,
 *       each containing ID sequence string and oLIST structures.
 * 

 * VAB.IMG is
 *  ** Player 0 image
 *   char[768]   -- palette
 *   uint16_t    -- length of following PCX compressed image
 *   image_data[] --
 *  ** Player 1 image
 *   char[768]   -- palette
 *   uint16_t    -- length of following PCX compressed image
 *   image_data[]
 * 
 * 

 * File: FSEQ.DAT
 * Desc: Indexes to video and audio files for failed mission stages.
 * Structure:
 *       50 Table structures
 *       sequence of oFGROUP structures,
 *       each containing ID sequence string and oLIST structures.
 * 

 * File: REPLAY.DAT
 * Desc: Contains indices to animation sequences of past player missions.
 * Structure:
 *       sequence of ReplayItem structures,
 *       each containing offsets to animations.
 * 

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