Add the category "Modal-Logic"

[Mystelven]

In the file website/solvers.html :

Modal SAT solvers

{% include solverspanel.html title="Modal Logic Formulas solvers" tags="Modal-Logic" %}

Where can be add :

• InKreSAT : http://www.ps.uni-saarland.de/~kaminski/inkresat/
• StarSAT : http://www.mrg.dist.unige.it/~tac/StarSAT.html
• {all the other famous Modal reasoning solvers}

[Mystelven]

The Merge Request #18 is fixing this issue.