Stop the sulk with GPL2016 on Windows (#602)

* Fixes for VS2017.
* Added a getopt implementation.
* Added a unistd.h.
* Corrected closing of sockets for Windows versions.
* Fixed gdbserver CMakeLists.txt to play nice with VS2017.
* Fixed include of getopt.h and unistd.h for WIN32.
* Added a unistd.h.
* Corrected closing of sockets for Windows versions.
* Fixed gdbserver CMakeLists.txt to play nice with VS2017.
* Override /MD to /MT for MSVC to match libusb's builds.
* MSVC settings should be if (MSVC).
* Don't busy-wait for long periods in usleep().
* Dynamic link to MSVC libusb binaries.
* Added Visual Studio section to compiling.md.
* Added -D_CRT_NONSTDC_NO_WARNINGS to MSVC flags.
* Prevented some more warnings under MSVC.