hameg-hmo: Move the declaration of the driver info out of protocol.h

This fixes duplicate symbol error on Mac OS X.

BugLink: http://sigrok.org/bugzilla/show_bug.cgi?id=216
serial-dmm: Commented struct dmm_info.
serial-dmm: Add BBC Goerz Metrawatt M2110 DMM driver.
bbcgm-m2110: Minor cosmetics.
Bump minimum libusb version to 1.0.16

This gets us the libusb version checking mechanism itself, hopefully
making this sort of thing easier in future.

Also hotplug, device tree traversal, and lots of fixes.
Use new libserialport event set API to make GPollFDs for serial sources.
Use common usb_source_add and usb_source_remove functions.
Implement usb_source_add and usb_source_remove for Windows.
Winsock2.h must be included before anything that includes Winsock.h.
Windows usb: Unlock mutex when shutting down wait thread.
usb: Enforce that there can only be one USB event source for now.
Windows usb: don't try to resume thread if shut down in callback.
demo: Code cleanup.
add support for AVG mqflag
endian neutral helper macro to read 16/32 bits integer from unaligned memory
appa-55ii: Initial driver skeleton.
appa-55ii: driver implementation with Live and Memory data source support
appa-55ii: Coding style fixes.
gmc-mh-1x-2x: Cosmetics, whitespace, cleanups.
gmc-mh-1x-2x: Fix two compiler warnings.