With the recent CMake cleanup, getting raylib's dependencies for use
when building rlgl_standalone is quite straight forward, so lets enable
it again.

Fixes #508, just properly this time. :)

Remove that link_libraries_to_executable() hack and defines a proper
raylib target that can be used with target_link_libraries.

The same target is also available for external (user) code by using
find_package(raylib).

This results in:

- Remove hardcoded build directories from examples and games CMakeLists.txt
- Allow rlgl_standalone and other special examples to be built easily
- Allow CMake projects to find_package(raylib instead of fiddling with pkg-config
- Makes code a little more maintainable
- Fixes #471, #606.
- Makes code less confusing by removing the double use of PLATFORM (#584).

Note that this is still not _The Right Way_(TM), because normally
raylib-config.cmake (or its includes) would be automatically generated.
I didn't manage to get that to work though, so I went the easier route
of just wrapping pkg_check_modules for consumption by find_package.

1. Always synthesize a complete frame of audio, using a second buffer (this prevents gaps in playback)
2. Sine is computed correctly, with an adjustable frequency
3. User can modulate frequency in real-time with mouse
4. Entire audio buffer data is shown, visually demonstrating how sine changes in wavelength

Closes #588.

Mimic the Makefile by outputting html + js instead of LLVM IR.

Still a work in progress but it already works...
Current riqm API could be simplified...

GLSL 1.10 is typesafe ([PDF specs](https://www.khronos.org/registry/OpenGL/specs/gl/GLSLangSpec.1.10.pdf), page 22), so this shader will not load properly during build.

It's not a super important change, but I came across it while playing with the examples on my pi.

Examples can be compiled for web with no code change at all! Usually
examples need to be refactored for web... using emscripten code
interpreter (emterpreter), it can manage synchronous while() loops
internally... as a downside, execution is very slow...

Now it works with mini_al library

No model available, this example should probably be redesigned...

Oculus API has changed so much that it has no sense to keep this example here... it was funny to test it in the past...

This change allows rlgl.h usage as independent single-file header-only module... still some tweaks required, like removing GLAD dependency... required extensions could be manually loaded!

Also removed shader_distortion.h, embedded in rlgl.h

Fixes: c3b948b1 ("Replaced skybox HDR image")

Replaced old dwarf model

Note that HDR exposured possibilities are not used on this example...

Replaced by medieval 3d assets

It seems TCC was not casting correctly int values to float in some
specific situations

src/core.c does explicitly skip including <camera.h> on Android
and tests fail. Therefore skip these failing tests.

Closes #507.

Currently, if:
* GCC doesn't supports -no-pie: Build error
* GCC supports -no-pie
    * GCC is not configured with --enable-default-pie: No-op
    * GCC is configured with --enable-default-pie:
            Slightly worse performance because we still generate -fpie code
            (-pie affects linker, -fpie affects compiler)

So instead of probing for existence of -fno-pie -no-pie, remove it altogether.

Fixes #540: Build breakage on Debian 8 with gcc 4.9.

Review raylib_icon resource

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