applet.memory.24x: use argparse subparsers. Instead of mutually exclusive groups. Also, handle errors.

applet.memory.25x: remove default for ADDRESS and LENGTH arguments. These need to be specified explicitly anyway in virtually all cases.

applet.interface.i2c_master: use argparse subparsers. Instead of mutually exclusive groups.

applet.interface.jtag_probe: special-case IR segmentation with 1 TAP.

*.xc9500→*.xc9500xl The XC9500 and XC9500XL series have completely different programming interfaces, and rather large other differences as well.

applet.program.avr→applet.program.avr.spi Also, describe the Atmel programming interface mess.

database.atmel.avr: extract from applet.program.avr.

database.xilinx.xc9500: separate devices and devices_by_idcode.

applet: use dedicated *Error for each *Interface class we have. This makes *Interface classes more reusable, in preparation for things like exporting them as a set of RPC calls. Also, rename a few *Interface classes to be more descriptive of what they do.

applet..i2c_master: pad scanned addresses to 7 bits.