parse optional URI parameters

Allow setting drive 0 an drive 1 disk contents, the ROM type, and
whether the "AUTO" key is automatically pressed 3 seconds after reset
(enough time for the boot up sequence).  This allows a single URL to
invoke the emulator and launch the menu program with a specific floppy
image, eg

ccemu.html?cd0=disks/airraid.ccvf&auto=1