Now `BeginTextureMode()` does not clean buffers automatically, that behaviour has been changed because there could be some case (i.e. painting software) where texture buffer does not ned to be cleared; user is responsible of clearing buffers using `ClearBackground()`

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

It's more educational to go through new material system, so, I decide to
remove this function to avoid students confusion...

Functions renamed to improve library consistency

Now it's possible to render to texture, old postprocessing system will
be removed on next raylib version.

Cat replaced by dwarf

Examples have been renamed for coherence with raylib modules and test
examples have been merged into examples folder.

View CHANGELOG for details