[mizar] Open-sourcing Mizar

[Adam Naumowicz <adamn@math.uwb.edu.pl>]

Dear Mizar Users,

I'm writing to let you know that the source code of the current Mizar 
implementation is now available as a public repository at

https://github.com/MizarProject/system

The Board of Control of the Association of Mizar Users who is the 
copyright holder, including Czeslaw Bylinski who is the main 
implementer and author of the sources decided to have it open-sourced
under the GNU GPLv3 license. This should allow accessing the code and 
developing Mizar-related software on similar terms as the Mizar 
Mathematical Library (available under both GPL and CC-By-SA licenses).

Best regards,

Adam Naumowicz