Some distros (a 4-letters) don't have icotool.
Let's ship the .ico in the tarball.
The build will fail if icoutil is not installed when
building from git or when the .ico is absent. The error
should be explicit.
This makefile is just fantastic, it forces you into good practices,
support various build targets (my windows builddir ignore the right
files etc..)
The more I use it, the more I like it.
