#789 kiwix-index as multithreaded application.

[Alberto Guzmán]

Develop a kiwix-index as a multithreaded application, so newer processors (multi-core) can use full potential in order to index the increassing size ZIM files.

It might be complicated since kiwix supports all the common OS available, but still i think is a feature that is needed.

[Emmanuel Engelhart]

kiwix-index is already multi-threaded.