Error check using IsValid functions and return error unions (#191)

* Verify shaders are valid

* Verify images are valid

* Verify models are valid

* Verify materials are valid

* Verify textures are valid

* Verify render textures are valid

* Verify waves are valid

* Verify sounds are valid

* Verify music is valid

* Verify audio streams are valid

* Verify fonts are valid

* Update examples to handle error unions

examples/textures/textures_image_loading.zig

@@ -25,8 +25,8 @@ pub fn main() anyerror!void {
 
     // NOTE: Textures MUST be loaded after Window initialization (OpenGL context is required)
 
-    const image = rl.loadImage("logo/logo.png"); // Loaded in CPU memory (RAM)
-    const texture = rl.loadTextureFromImage(image); // Image converted to texture, GPU memory (VRAM)
+    const image = try rl.loadImage("logo/logo.png"); // Loaded in CPU memory (RAM)
+    const texture = try rl.loadTextureFromImage(image); // Image converted to texture, GPU memory (VRAM)
     // Once image has been converted to texture and uploaded to VRAM,
     // it can be unloaded from RAM
     rl.unloadImage(image);