Fix GTest library location on Windows.
On Windows, use the correct version of the C++ runtime.
Add basic compiler flags on Windows.

Add warnings, optimization settings, and the NOMINMAX define (required
for a Qt header to compile on Windows).
Reduce warnings to level 3 on Windows.
Force MSVC to use static version of the CRT.

Shloud fix issues with the linker with GTest dependency on the static
CRT when built as a static library.
Fix downloading GTest occuring too late in the build process on Windows.
Update README.

[skip ci]
Merge pull request #42 from Neki/topic/bf_fix_cmake_conf_for_windows

CMake configuration on Windows.