Strangely, there are already some footprints for USB micro connectors
in the Connectors_USB library:
https://github.com/KiCad/Connectors_USB.pretty
but I couldn't find any schematic symbols for a micro USB connector.
(USB micro B and mini B connectors have an additional pin, the ID pin,
which is not present in the traditional USB B connector, so the
existing USB_B symbol can't be used.)
So, I have added a symbol USB_B_Micro, based on the existing USB_B
symbol. I've also added USB_B_Mini as an alias for USB_B_Micro,
because the micro and mini connectors have the same pinout.
The pinout is here:
http://pinouts.ru/PortableDevices/micro_usb_pinout.shtml
