New maintainers of containers

[Milan Straka]

Hi David and Edward,

following the announcement and small discussion at libraries at haskell,
I have added you both as maintainers of containers on github and on
hackage. The idea is that David will take care of Data.Sequence,
and CLC will manage the rest (at least until someone else appears,
like wren).

I have added only you Edward on behalf of CLC, but you can add others if
you like (you should have the rights to do it).

I would like to note that since containers are widely used and needed by
GHC itself, I consider the CLC to have the final word if any
disagreement ever arises between CLC and other container maintainers
(David, wren, ...). Also please consider backward compatibility very
highly.

I will stop reading libraries at haskell and also containers github
notifications soon, but feel free to write me an email or mention
me on github (using @foxik) if you need to contact me.

Cheers,
Milan Straka