Allows SVGRenderer to export the result from memory

Fixes #120

Author: arguiot

Sources/SVGRenderer/SVGRenderer.swift

@@ -231,13 +231,20 @@ public class SVGRenderer: Renderer{
     public func drawOutput(fileName name: String) throws {
         try savePlotImage(fileName: name)
     }
+    
+    /// Returns the content of the SVG generated by the renderer
+    public var svg: String {
+            // Build the document.
+            let header = #"<svg height="\#(imageSize.height)" width="\#(imageSize.width)" version="4.0" xmlns="http://www.w3.org/2000/svg" xmlns:xlink= "http://www.w3.org/1999/xlink">"#
+                + "\n" + #"<rect width="100%" height="100%" fill="white"/>"#
+            let font = #"<defs><style>@import url("https://fonts.googleapis.com/css?family=\#(fontFamily)");</style></defs>"#
+            let image = header + "\n" + font + "\n" + lines.joined(separator: "\n") + "\n</svg>"
+            return image
+    }
 
     func savePlotImage(fileName name: String) throws {
         // Build the document.
-        let header = #"<svg height="\#(imageSize.height)" width="\#(imageSize.width)" version="4.0" xmlns="http://www.w3.org/2000/svg" xmlns:xlink= "http://www.w3.org/1999/xlink">"#
-            + "\n" + #"<rect width="100%" height="100%" fill="white"/>"#
-        let font = #"<defs><style>@import url("https://fonts.googleapis.com/css?family=\#(fontFamily)");</style></defs>"#
-        let image = header + "\n" + font + "\n" + lines.joined(separator: "\n") + "\n</svg>"
+        let image = self.svg
 
         let url = URL(fileURLWithPath: "\(name).svg")
         try image.write(to: url, atomically: true, encoding: .utf8)