Added support for render to texture (use RenderTexture2D)

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

examples/resources/shaders/bloom.fs

@@ -1,11 +1,12 @@
 #version 330
 
 in vec2 fragTexCoord;
+in vec4 fragTintColor;
 
 out vec4 fragColor;
 
 uniform sampler2D texture0;
-uniform vec4 fragTintColor;
+//uniform vec4 fragTintColor;
 
 // NOTE: Add here your custom variables