Multiple updates.

- Added a new project that shows how to use the library.
- Implemented a sample that uses the WMI interface.
- Updated the gitignore patterns.
Added amd64 build for the test project.
Multiple updates.

- Defined the return type of enumerate_dxgi_units funtion.
- Added some more data members to the DXGIUnit class.
First version of DXGIUnit's interface.

- Added all the ctors, dtor and methods.
- Improved the member data.
Multiple updates.

- Implemented the inline functions of DXGIUnit class.
- Commented the DXGIUnit interface.
Multiple updates.

- dll-exported the std::wstring implementation used by DXGIUnit class.
- Documented the WMIUnit class and the enumerate_wmi_units function.
Multiple updates.

- Fixed a compilation issue in one of the inline functions of
  DXGIUnit class.
- Fully implemented the DXGIUnit class and the enumerate_dxgi_units
  function.