Review raylib_icon resource

Panders to the idiosyncrasies of my work flow:
I have my raylib build directory mounted as a VirtualBox vboxfs for use
with my Linux VM, but vboxfs doesn't support symlinks, while raylib shared
library versioning on Unix expects symlinks to work.
If this happens, library versioning is now disabled on Unix with
an error message instead of just failing the build.

Less maintenance overhead that way,
given that make/CMake now also do library versioning.

They were disabled because they failed to build,
but this patch set fixes the build on Linux and macOS.

This doesn't apply to the AppVeyor build on Windows yet;
it currently fails at linking with OpenAL.

Support Universal Windows Platform (UWP):
- Windows 10 App
- Windows Phone
- Xbox One

OpenAL Soft and raylib compiled for release and stripped

Some people might find this handly

Added loader webs (previously ignored)

and add instructions in physac examples to run it successful.