Implement --contains flag for branch list

[nesterov-n]

Hello.

I implemented '--contains' param for branch list command.

[ajoberstar]

Thanks for putting this together. One change I think would be benficial is making contains an Object, so it could be a Grgit Commit instance or some other representation of a revision. If you look at TagAddOp I'm using that pattern for the pointsTo object (and use the toRevisionString method to convert it back to a string).

[nesterov-n]

@ajoberstar Done

[ajoberstar]

Great! Thanks again.

[nesterov-n]

@ajoberstar When do you plan release new version of your lib? I really need this feature for my build system :)

[ajoberstar]

1.6.0-rc.1 is out now

[nesterov-n]

Great! Thanks a lot