* Fix bug #1270

Added an argument to the shader in order to flip the texture

* Fix Bug #1270

* Fix bug #1270

Note this example is not working properly, it still requires some review.

All data should be properly initialized by now

They are not automatically unloaded when unloading the model!

- Mesh, Shader, Material structs have been reviewed to minimize size when passed by value, all required code has been reviewed.
 - GetCollisionRayModel() reviewed to avoid pointer, not required because model is not modified inside the function
 - UnloadMesh() reviewed, pointer not required
 - CheckCollisionRay*() parameters name reviewed

* Fix loading multiple animations from .iqm file

* Fix memory leak in models_animation example

* Added export instructions to the animation example

* use raylib free

* include <stdlib.h> to appease the travis CI gods

* replace tabs with spaces

When using FormatText() several times in same function, returned string is static and so, the same is returned, resulting in failures on shader loading.

Redesigns, deletes and renames

Also noted authors propertly on contributed examples

Added walls collision check

Some tweaks

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.

Multiple functions added and some reviewed to adapt to the new multi-mesh, multi-material and animated models.