libusb's header must be named usb.h.

The current libusb package installs it as usb0_usb.h, which is incorrect.
For other packages to actually be able to use the installed libusb, the
header file must be named usb.h.
add initial bash completion to tools/
add mxe alias and path to completion script
rename completion script to mxe-activate and unset env vars
Merge pull request #115 from uwehermann/libusb-fix

libusb's header must be named usb.h.
Merge branch 'master' into multi-rebase