Setup the thirdparty "freetype" library, on Windows.

Usage:
  v setup-freetype

This command only does anything on Windows; on other systems it just
prints a reminder message and exits.

It checks whether `thirdparty/freetype` is present in the V
installation, and if it is not, clones
https://github.com/ubawurinna/freetype-windows-binaries into it.

Freetype is needed for drawing text by several of the graphical
examples, so run this command if building them fails with linker
errors mentioning freetype.
