add script to re-generate all examples

Output File (`example_chart.svg`):

![A simple line chart](./examples/linecharts/examples_lines_with_points.png?raw=true)

![A simple line chart](./examples/linecharts/lines_with_points.svg)

Input File (`example_chart.plot`):

width: 1200px;

height: 480px;

plot {

  axis-top: off;

  axis-right: off;

  margin: 0px;

  margin-top: 1.1rem;

  margin-bottom: 2.6rem;

  margin-left: 5rem;

  margin-right: 3.4rem;

  ymin: -10;

  ymax: 32;

  xdomain: categorical;

  xdomain-format: string;

  series {

    title: "New York";

    xs: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec;

    ys: -0.2, 0.8, 5.7, 11.3, 17.0, 22.0, 24.8, 24.1, 20.1, 14.1, 8.6, 2.5;

    point-size: 3.3pt;

  }

  series {

    title: "Beijing";

    xs: Jan, Feb, Mar, Apr,  May,  Jun,  Jul,  Aug,  Sep,  Oct,  Nov, Dec;

    ys: -4, -1.4, 5.4, 13.5, 19.9, 24.3, 26.3, 24.9, 19.9, 13.1, 4.7, -1.8;

    point-size: 3.3pt;

  }

  series {

    title: "Москва";

    xs: Jan,  Feb,  Mar,  Apr, May,  Jun,  Jul,  Aug,  Sep,  Oct, Nov, Dec;

    ys: -7.4, -5.8, -0.1, 7.1, 14.7, 17.7, 20.6, 18.8, 12.6, 6.1, 1.1, -3.6;

    point-size: 3.3pt;

  }

  series {

    title: "Berlin";

    xs: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec;

    ys: -0.9, 0.6, 3.5, 8.4, 13.5, 17.0, 18.6, 17.9, 14.3, 9.0, 3.9, 1.0;

    point-size: 3.3pt;

  }

}

IMPORT TABLE city_temperatures

   FROM 'csv:examples/data/city_temperatures.csv?headers=true';

DRAW LINECHART WITH

   AXIS LEFT

   AXIS BOTTOM

   LEGEND TOP LEFT INSIDE;

SELECT

   city AS series,

   month AS x,

   temperature AS y,

   "Avg. Temperatures in " + month + " in " + city + ": " + temperature as label,

   "circle" as pointstyle

   FROM city_temperatures;

#!/bin/bash

set -uex

cd "${0%/*}"

find -name "*.plot" | while read f; do

  plotfx --in "$f" --out "${f/.plot/.svg}"

done