improved device enumeration to open every device, reset it, and get serial number; implemented methods to get serial number and open device by serial number; fixes #21
fixed SIGINT shutdown problem
fixed problem during device enumeration, if device is already open
moved usb device reset from enumerateDevices() to openDevice() otherwise there are problems if multiple processes use libfreenect2 to access different Kinects
Merge branch 'master' into fix_device_enumeration

Conflicts:
	examples/protonect/src/libfreenect2.cpp
Merge pull request #29 from christiankerl/fix_device_enumeration

enhance device enumeration
 - implements the methods to get device serial numbers and to open a device identified by its serial number
 - resets device inside openDevice method