Version 1.0 of the arena

A space in the pattern seems to be causing trouble

Former-commit-id: afa3088

Changed the diff checker to print the first 512 bytes from the diff o…

…utput. The rest of the output is discarded.

Bug fixes of some exceptions

Fixed a bug in the checkers

Former-commit-id: de9bbe7

Removed the Pascal language from the solution language selection.

Former-commit-id: 9e7d2f2

Latest changes went in production:

* the grader supports checkers
* the graders does not sleep if there is work to be done
* the results are world viewable
* the results are with smaller font