Masahiro Nakagawa and SHOO invited to join Phobos developers

[SHOO]

Andrei Alexandrescu さんは書きました:
> Thanks! You are now a Phobos developer.
I'm happy to join member of Phobos developer!

 > Unfortunately you cannot commit
> your changes to std.date because it infringes on Tango's license.
> 
> Andrei

What did I infringe the license of Tango for? For interfaces? For 
implements?
I've written the codes without the intention. Please tell me the points 
that are the problem.