fix example links on introduction page

  html = TPL.render(tpl, env)

  write_page(path, html)

  copy_file(path + "/output.svg", os.path.join("examples", url + ".svg"))

  copy_file(path + ".svg", os.path.join("examples", url + ".svg"))

def build_example_list(examples):

  tpl = """

<h1>Example: <code>{{example_url}}</code></h1>

<h4>Output File:</h4>

<img src="output.svg" />

<img src="/examples/{{example_url}}.svg" />

<h4>Source File:</h4>

<pre><code>{{example_src}}</code></pre>

<div style="height: .6em;"></div>

_Example: Simple timeseries chart_

<a href="/examples/linecharts/simple_lines"><img src="/examples/areacharts/examples_simple_lines.png" style="width: 100%;" /></a>

<a href="/examples/linecharts/simple_timeseries"><img src="/examples/linecharts/simple_timeseries.svg" style="width: 100%;" /></a>

_Example: Chart with explicit domain and legend_

<a href="/examples/linecharts/explicit_domain"><img src="/examples/linecharts/examples_explicit_domain.png" style="width: 100%;" /></a>

<a href="/examples/linecharts/explicit_domain"><img src="/examples/linecharts/explicit_domain.svg" style="width: 100%;" /></a>

_Example: Horizontal barchart_

<a href="/examples/barcharts/horizontal_bars"><img src="/examples/barcharts/examples_horizontal_bars.png" style="width: 100%;" /></a>

<a href="/examples/barcharts/horizontal_bars"><img src="/examples/barcharts/horizontal_bars.svg" style="width: 100%;" /></a>

_Example: Scatter chart with lables_

<a href="/examples/pointcharts/pointchart_with_labels"><img src="/examples/pointcharts/examples_pointchart_with_labels.png" style="width: 100%;" /></a>

<a href="/examples/pointcharts/pointchart_with_labels"><img src="/examples/pointcharts/pointchart_with_labels.svg" style="width: 100%;" /></a>

<script async defer src="https://buttons.github.io/buttons.js"></script>