Support @font-face on Windows

[liZe]

I've successfully made @font-face work on Windows (using fontconfig too) with small changes:

• I've removed if sys.platform.startswith('win') from fonts.py.
• I've added 'libfontconfig-1' in dlopen for fontconfig (we can probably remove 'fontconfig' or 'libfontconfig') in fonts.py.
• I've created a file called fonts.config with the content from Fontconfig error: Cannot load default config file shoes/shoes3#46.
• I've set the environment variable FONTCONFIG_FILE to the config file path.
• I've added a try/except block around fonts.py's clean (removing the temporary files) because Windows says that the file is used by another process. (see OSError: Too many open files #396).

With these changes, @font-face works, but some problems remain:

• We have to find a reliable way to create and make fontconfig use fonts.config.
• We have to find a way to make this file accurate (find folders containing fonts used by Windows, depending on how Windows is installed).

If anyone is interested in solving this problem, I can provide some help (as long as the question is not related to Windows 😄).