Add members to a card

[tbreeds]

It'd be great to be able to do something like
trellotool card addmember $bob to add key people to the card ; or
trellotool card add ... --with-me to add yourself as a member of the card at creation time

Probably means we also need
trellotool member * to list members

[mrda]

Can I suggest the following API?

trellotool card member add <username>, where could be the uuid or member.username or "me"?

This will require defining the of the current user. It seems we might need to look at all members who are on the board, and allow the user to select which one is themselves.

trellotool member list is probably what we want to list members.

All good ideas - I look forward to your PR :-)