Generalized core:image loader

```odin
import "core:image"
import "core:image/png"

...

img, err := image.load_from_file("path.png")
```

core/image/general_loader.odin

@@ -0,0 +1,39 @@
+package image
+
+import "core:mem"
+import "core:os"
+
+Loader_Proc :: #type proc(data: []byte, options: Options, allocator: mem.Allocator) -> (img: ^Image, err: Error)
+
+@(private)
+_internal_loaders: [Which_File_Type]Loader_Proc
+
+register_loader :: proc(kind: Which_File_Type, loader: Loader_Proc) {
+	assert(_internal_loaders[kind] == nil)
+	_internal_loaders[kind] = loader
+}
+
+load :: proc{
+	load_from_slice,
+	load_from_file,
+}
+
+load_from_slice :: proc(data: []u8, options := Options{}, allocator := context.allocator) -> (img: ^Image, err: Error) {
+	loader := _internal_loaders[which(data)]
+	if loader == nil {
+		return nil, .Unsupported_Format
+	}
+	return loader(data, options, allocator)
+}
+
+
+load_from_file :: proc(filename: string, options := Options{}, allocator := context.allocator) -> (img: ^Image, err: Error) {
+	data, ok := os.read_entire_file(filename, allocator)
+	defer delete(data, allocator)
+	if ok {
+		return load_from_slice(data, options, allocator)
+	} else {
+		img = new(Image, allocator)
+		return img, .Unable_To_Read_File
+	}
+}