title: Issue with CharacterCache in piston_window in Rust
body: <p>I am currently working on a project in Rust with the piston game engine (Using piston_window version 0.123.0) and I am having an issue with rendering text. The draw function returns an error fro a non implemented trait.</p>
  <p>Here is the code:</p>
  <pre><code>// Get font for text rendering
  let font = include_bytes!(&quot;font\\UbuntuMono-B.ttf&quot;);
  let glyphs = Glyphs::from_bytes(font,
      window.create_texture_context(),
      TextureSettings::new())
      .unwrap();
  </code></pre>
  <p>Which is passed through a function:</p>
  <pre><code>Draw::render(&amp;mut window, &amp;event,
               &amp;game.matrix,
               &amp;game.frame_counter,
               &amp;mut glyphs)
  </code></pre>
  <p>To this function:</p>
  <pre><code>pub fn render(window: &amp;mut PistonWindow,
                event: &amp;Event, matrix: &amp;Matrix,
                frame: &amp;i32, glyphs: &amp;mut Glyphs)
  {
      // Stuff
  }
  </code></pre>
  <p>Where the text rendering occours:</p>
  <pre><code>Text::new_color(WHITE, 12).draw( // The draw() here is highlighted red for the error
       &quot;Hold&quot;,
       &amp;mut glyphs,
       &amp;context.draw_state,
       context.transform
            .trans(184.0, 38.0),
       graphics
  )
  </code></pre>
  <p>And returns the error message:</p>
  <pre><code>the trait bound `&amp;mut piston_window::glyph_cache::rusttype::GlyphCache&lt;'static, piston_window::TextureContext&lt;gfx_device_gl::factory::Factory, gfx_device_gl::Resources, gfx_device_gl::command::CommandBuffer&gt;, piston_window::Texture&lt;gfx_device_gl::Resources&gt;&gt;: piston_window::CharacterCache` is not satisfied
  
  the trait `piston_window::CharacterCache` is not implemented for `&amp;mut piston_window::glyph_cache::rusttype::GlyphCache&lt;'static, piston_window::TextureContext&lt;gfx_device_gl::factory::Factory, gfx_device_gl::Resources, gfx_device_gl::command::CommandBuffer&gt;, piston_window::Texture&lt;gfx_device_gl::Resources&gt;&gt;`
  
  help: the following implementations were found:
          &lt;piston_window::glyph_cache::rusttype::GlyphCache&lt;'b, F, T&gt; as piston_window::CharacterCache&gt;
  </code></pre>
  <p>Any help with how to fix this error would be appreciated. I apologise if I have given too much/little or incorrect info for this issue, I am not too familiar with StackOverflow.</p>