Added Subpaths to bezier-rs (#730)

* Added Subpath constructor, iterator and length

* Asserted that subpaths of len < 2 cannot be closed. Added len() and comments

* Added subpath to_svg(), made structs public, made quadratic use either in_handle or out_handle

* add bezier handles

* Added basic interactivity and index traits

* Added SubPath interactivity

* Added svg styling

* Broke subpath impl across multiple files. More sylistic changes per review

* Fixed format error

* Added closed subpath to documentation page

* Modified subpath to_svg to use functional style

* Stylistic changes per review

* Fixed build errors

* More sylistic changes per review

* Moved svg commands to constants

* Moved formatting for svg arguments to ToSVGOptions

* Renamed files in git

* Even more stylistic changes per review

bezier-rs/docs/interactive-docs/wasm/src/svg_drawing.rs

@@ -0,0 +1,11 @@
+// SVG drawing constants
+pub const SVG_OPEN_TAG: &str = r#"<svg xmlns="http://www.w3.org/2000/svg" width="200px" height="200px">"#;
+pub const SVG_CLOSE_TAG: &str = "</svg>";
+
+// Sylistic constants
+pub const BLACK: &str = "black";
+
+/// Helper function to create an SVG text entitty.
+pub fn draw_text(text: String, x_pos: f64, y_pos: f64, fill: &str) -> String {
+	format!(r#"<text x="{x_pos}" y="{y_pos}" fill="{fill}">{text}</text>"#)
+}