rendering: Simplify Cairo context usage, remove unneeded calls.

Moved Cairo context usage to Rust, and rearranged ctx setup (position) to happen in one place.

Removed render calls that were overwritten on each draw call anyway.

src/keyboard.rs

@@ -11,7 +11,7 @@ use ::action::Action;
 use std::io::Write;
 use std::iter::{ FromIterator, IntoIterator };
 
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub enum PressType {
     Released = 0,
     Pressed = 1,