Copy more fields

[ykgoon]

Improve proposal

More keybindings:

• b to copy user name
• u to copy URL

These keys are mapped similar in GUI client. They are frequently used (at least I do). Without a keybindings I have go into the entries and copy them with a lot of keystrokes.

Meantime as keybindings grow, there should be a better way to display instructions. I propose these be displayed either on top or bottom of the buffer.

[ifosch]

About the way to display instructions, I think it should be similar to what magit does for that.