Cleanup all the backends

Author: 38

examples/gtk-demo/Cargo.toml

@@ -7,7 +7,8 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-plotters = {path = "../..", features = ["cairo"]}
+plotters = {path = "../.."}
+plotters-cairo = "0.1.*"
 cairo-rs = "0.8.1"
 gtk = "0.8.1"
 gio = "0.8.1"

examples/gtk-demo/src/main.rs

@@ -6,6 +6,7 @@ use gtk::DrawingArea;
 
 use cairo::Context;
 use plotters::prelude::*;
+use plotters_cairo::CairoBackend;
 
 fn build_ui(app: &gtk::Application) {
  drawable(app, 500, 500, |_, cr| {