Add function example

Author: milliams

examples/function_svg.rs

@@ -0,0 +1,8 @@
+extern crate plotlib;
+
+fn main() {
+    let f = plotlib::function::Function::new(|x| x, 0., 10.)
+        .style(plotlib::function::Style::new().colour("burlywood"));
+    let v = plotlib::view::View::new().add(&f);
+    plotlib::page::Page::single(&v).save("function.svg");
+}