fteeprom-{erase,prog}: detach logic: change to detach by default As it turns out, detaching all ttyUSB interfaces of a multichannel device does not require outside knowledge of how many channels there are, as in our previous -d option design that is being removed here - instead we can read the bNumInterfaces constant from the USB device's config descriptor and thus know how many interfaces there are in total. Based on this discovery, change the design of fteeprom-{erase,prog} as follows: * remove -d option; * flip the default to where we detach all interfaces by default; * add -n option to NOT detach any interfaces.

This code repository is a work in progress.  The initial objective is to move
FTDI EEPROM tools out of freecalypso-hwlab Hg repository and polish them into
an installable software component similar to other FreeCalypso tools; I am also
looking at the possibility of developing some tools for old-style CP2102 chips
that require EEPROM tinkering in order to switch between 230400/460800/921600
and 203125/406250/812500 baud rates.