New build system

Using new build script system for all platforms. 

- `openssl-sys` prototype taken [alexcricton's repo](https://github.com/alexcrichton/openssl-sys) but embedded as it should be much easier to develop while it's in-tree rather than in a separate repo. 

- dropped all external links but Windows ones. I'm not sure how it is correct to proceed here as don't have access to Windows. Perhaps they could be dropped too as almost every windows app will be linked against `gdi32` and `win32`, `wsock32` may be not.
This should probably also move into the build script checking `os::getenv("TARGET")` to see if it contains `windows`