Add option for disabling windows compilation warn

[Nicogene]

It fixes #40

[traversaro]

Ok for me, but consider that the /Wall option is not recommended by MSVC documentation them-self, see https://docs.microsoft.com/en-us/previous-versions/thxezb7y(v=vs.140)?redirectedfrom=MSDN. The recommended setting is /W4, not /Wall. For example, one problem is that Wall also generate warnings by just including the standard headers (see https://stackoverflow.com/questions/4001736/whats-up-with-the-thousands-of-warnings-in-standard-headers-in-msvc-wall).