Why am I still supporting this???

...disposing RenderTexture.

[textures] Added SaveKTX()
[rlgl] Exposed rlGetGlTextureFormats()

When a batch reach its vertex limit, a draw call is issued and batch restarted for refilling but if the draw call was issued for vertex data accumulated inside rlPushMatrix/rlPopMatrix, draw call was issued before the rlPopMatrix, consequently modelview matrix was not properly recovered before the draw call... obviously, it only happened the following draw calls, not the first one...

Now it works ok but this system needs to reviewed, noticed and important frames drop when processing around 20 dynamic batch draw calls, it means filling MAX_QUADS_BATCH (8192) quads of data 20 times per frame, including data updating and sending for draw processing.

Doing some maths, it means:
Vertex data (float) -----> 8192 quads * 4 vertex * 3 comp * 4 byte = 393216 bytes
Texcoords data (float) -> 8192 quads * 4 vertex * 2 comp * 4 byte = 262144 bytes
Color data (uchar) -----> 8192 quads * 4 vertex * 4 comp * 1 byte = 131072 bytes

Thats a total of 786432 bytes (0.75MB) sent to GPU 20 times per frame for processing... I'm testing in an Intel HD Graphics integrated, I imagine is too much data to be sent and and it causes stalls, so the frames drop...

Corrected memory leak!

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

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

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).

Added struct Vector4 for convenience

- Renamed enum TextureFormat to PixelFormat for consistency
- Added support for pixel format UNCOMPRESSED_R32
- Using GetPixelDataSize() where required

To be more generic and configurable

Requires some work, distortion shader could be move out of raylib to
example code...

Now it should be coherent with OpenGL math standards

Exposed some raymath useful functions to raylib API

...to avoid possible conflicting symbols

Moved to custom example, now raylib only supports simulated VR
rendering.
Oculus code was too device dependant... waiting for OpenXR.