Show ref object type in the commit list

[Chitoku]

The current object list lacks what kind of ref object they are as follows:

$ git rebase **
>
  5/5
> another-branch   2nd commit
  master          1st commit
  v1              1st commit
  v2               2nd commit
  3e209a3         1st commit

To effectively filter those references, object types (printed in green) can be shown like this:

$ git rebase **
>
  5/5
> another-branch  branch   2nd commit
  master          branch  1st commit
  v1              tag     1st commit
  v2              tag      2nd commit
  3e209a3         commit  1st commit

which results in:

$ git rebase another-branch

[Chitoku]

Resolved in #72