Users can define their custom memory management macros.
NOTE: Most external libraries support custom macros in the same way, raylib should redefine those macros to raylib ones, to unify custom memory loading. That redefinition is only implemented as example for stb_image.h in [textures] module.
Issue was related to vertex tangent attibutes not uploaded to GPU, a quick solution was implemented for new vertex attributes loading for already existing meshes... I don't like it specially but it will work for now.
If we have no data to update/draw, we avoid update/draw. On `DrawBuffersDefault()` if no vertes data is available nothing is drawn but some globals: vertexData, projection, modelview, draws... are reseted.
There shouldn't be any problem if we don't touch those globals in case no vertex have been processed but, just in case, I warn about it.
When drawing LINES or TRIANGLES, vertex are accumulated in same buffer as QUADS and new draw calls are registered but QUADS drawing uses an index buffer for optimization, so, when adding LINES/TRIANGLES vertices we need to make sure next draw calls for QUADS keep aligned with indices buffer.
To get that we just add some alignment vertex at the end of the LINES/TRIANGLES draw calls, to make them multiple of 4 vertex.
When capturing framebuffer, if some element with transparency has been drawn, it retrieves that data... it could be a bit annoying in some situations because we could expect color compositing with background color... It depends on the situation and our needs... but most of the time we don't want that transparency on screenshots.
Specific textures generation code is quite redundant and not flexible for the user, I'm trying to figure out some easy way to allow raylib users to do the same without needing those functions (very specific and shader dependant). RenderTexture loading and Cubemap textures support must be improved.
Problem aligning provided vertex data to multiples of four, because main buffer is intended to bu used with indexed quads... but also shared with triangles and lines.
