Headers cli flag

[bconnorwhite]

Added option to set headers through cli tool

[zhigang1992]

Can you add doc to readme? also would it be better to do -h 'Authorization: Bear abcd' instead. Better for commandline.

[bconnorwhite]

I forgot you can use the same flag multiple times with commander, I've adjusted this now to stack multiple headers:
... -H 'Authorization: Bearer abcd' -H 'Another: header'

Also added the header option to the README. I left the short flag as -H instead of -h though to avoid a collision with the -h help flag, but feel free to change this

[zhigang1992]

@helios1138 plz take a look. 😄