support tags

[andidevi]

This supports a tags field, which will contain an array of tags pointing to that commit.

[domharrington]

This looks good. Would you mind adding a more specific test to show what the output of this array would look like? I'm having a hard time figuring it out from looking at the code.

[andidevi]

This is just an array of strings containing the tag names add to that commit.

[andidevi]

The failing test is
returns C100 status for files that are copied
which seems pretty unrelated to my changes. It's sucessfully on my system, so I've no idea what to change.

[andidevi]

as its failing on nodejs 8 only it seems that this is an unrelated incompatibility of the C100 test.

[andidevi]

comparing to #36 it seems, that one must request more fields than only ['tags'] to keep the C100 test working on nodejs 8. so there are some hidden assumptions in the test/code that should be fixed there.

If not, you may accept #36 instead of this one.