Another round of polishing (#101)

* Implement basic refactorings

* Simplify some match statements

* Rename `ix` to `index`

If we're not going with a single letter name,
then a full word makes more sense.

* Rename `as_hex` to `to_hex`

`as_` implies lossless reinterpretation
while the function does a conversion that loses information

* Replace `for_each` with for loops

for loops are a lot easier to read and maintain.

* factor out x and y coords in Line::render

this is arguably more ergonomic

* Remove redundant `format!(format_args!())`

core/document/src/layers/folder.rs

@@ -13,11 +13,12 @@ pub struct Folder {
 
 impl LayerData for Folder {
 	fn render(&mut self, svg: &mut String) {
-		self.layers.iter_mut().for_each(|layer| {
+		for layer in &mut self.layers {
 			let _ = writeln!(svg, "{}", layer.render());
-		});
+		}
 	}
 }
+
 impl Folder {
 	pub fn add_layer(&mut self, layer: Layer, insert_index: isize) -> Option<LayerId> {
 		let mut insert_index = insert_index as i128;