Review raylib_icon resource

Makes it easier to support Wayland later on.

We need the CMake stuff for wayland configuration.
Otherwise, we would have to replicate that ourselves.
This is the full 7ef34eb06d tree except
for tests/ examples/ and docs/

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.

Try to avoid types conflict with Font

- Preparing MP3 files support
- Jumped version to raylib 2.0-dev (too many breaking changes...)

- Renamed Begin3dMode() --> BeginMode3D()
- Renamed Begin2dMode() --> BeginMode2D()
- Renamed End3dMode() --> EndMode3D()
- Renamed End2dMode() --> EndMode2D()

- Some examples tweaks
- Reviewed ImageFormat()
- Use float for text fontSize

Useful to parse raylib.h to generate raylib-lua and Notepad++
intellisense XML info

Just added a fallback in the meantime...

As stated in the note, I'm not sure if math is right, just followed a
reference implementation...

- Added Vector3OrthoNormalize() to raymath.h - not sure if it is correct
- Implemented MeshBinormals() - Mesh struct has not a place for them...
- Updated model_material_pbr example - tested but not working on my GPU
(old Intel HD), actually, it never worked on it...

Also added new compilation FLAGS for that pourpose

Allow compiling the library with support for automatic screen capture
(KEY_F12)

In case mesh loading fails, a cube is generated instead!

Seems tcc doesn't provide __sync_*. See #435.

Reported in #435, tcc generates out-of-line definitions for inline
symbols, something it shouldn't.  This fix punishes tcc for that
by making applications it compiles (slightly) larger...

Added raylib version to config

I would have liked config.h to be selected by include dir configuration,
but this way is less intrusive.

That way, a user needs only to touch a single file to configure what
features raylib is built with.
Include guards are left out intentionally, because config.h should only
be included in source files, not headers.

Later on, config.h can also define the raylib version (#461).

Now PLATFORM checks only used on core and utils modules

Renamed SaveImageAs() to ExportImage() for consistency on what actually happens with data.

Not sure if math is ok... just left a commented piece of code that uses pre-multiplied alpha.

Reviewed for PLATFORM_ANDROID and PLATFORM_UWP