Adding Ayan Sinha Mahapatra as a co-admin

[pombredanne]

Hi:
FYI, I have added Ayan Sinha Mahapatra @AyanSinhaMahapatra as an admin to this repo.
Ayan Sinha Mahapatra is well qualified and a long time user and contributor to intbitset and the maintainer of ScanCode toolkit which is one of the main users of intbitset.

@AyanSinhaMahapatra Thank for you help!