I keep trying to clean things up and needing std::strings. Might as
well just do this now.
usb_linux_client.c is going to stay as C because GCC isn't smart
enough to deal with the designated initializers it uses (though for
some reason it is in C mode).
The Darwin files are staying as C because I don't have a way to test
that they build.
The Windows files are staying as C because while I can actually build
for them, it's slow and painful.
Change-Id: I75367d29205a9049d34460032b3bb36384f43941
