Convert illustrations to PNG format.

src/epub/text/chapter-12.xhtml

@@ -89,19 +89,19 @@
 			<p>“Not so, O Bickley,” she answered, smiling again. “In the divine Oro’s head was the time set. You were the hand that executed his decree.”</p>
 			<p>When Bickley heard this I really thought he would have burst. However, he controlled himself nobly, being anxious to hear the end of this mysterious fib.</p>
 			<figure id="illustration-01">
-				<img alt="A dark, starry sky." src="../images/image-01.jpg" epub:type="z3998:illustration"/>
+				<img alt="A dark, starry sky." src="../images/image-01.png" epub:type="z3998:illustration"/>
 				<figcaption>Oro’s chart of the stars made by him about 250,000 years ago</figcaption>
 			</figure>
 			<figure id="illustration-02">
-				<img alt="The same sky, labeled with names of stars and constellations." src="../images/image-02.jpg" epub:type="z3998:illustration"/>
+				<img alt="The same sky, labeled with names of stars and constellations." src="../images/image-02.png" epub:type="z3998:illustration"/>
 				<figcaption>Key chart to the above</figcaption>
 			</figure>
 			<figure id="illustration-03">
-				<img alt="Another dark, starry sky, with many stars in different places." src="../images/image-03.jpg" epub:type="z3998:illustration"/>
+				<img alt="Another dark, starry sky, with many stars in different places." src="../images/image-03.png" epub:type="z3998:illustration"/>
 				<figcaption>Oro’s chart of the stars as he calculated that they would appear at his awakening</figcaption>
 			</figure>
 			<figure id="illustration-04">
-				<img alt="The new sky, labeled with names of stars and constellations." src="../images/image-04.jpg" epub:type="z3998:illustration"/>
+				<img alt="The new sky, labeled with names of stars and constellations." src="../images/image-04.png" epub:type="z3998:illustration"/>
 				<figcaption>Key chart to the above</figcaption>
 			</figure>
 			<p>“How long was the time that the lord Oro set apart for sleep?” I asked.</p>