gzip-compressed file indexer

 gztool indexes gzip-compressed files, allowing them to be accessed
 randomly (instead of from the beginning). It can index existing
 files, which takes as much time as decompressing the file entirely;
 it can also compress and decompress files itself, creating optimised
 indexes as it goes.
 .
 Other features include:
   - watch and index a gzip-compressed file as it is created;
   - partially extract a gzip-compressed file;
   - tail a gzip-compressed file (including follow mode).