Update <hgroup> children after first <h#> to <p>, ref. new HTML standard

src/epub/text/chapter-1.xhtml

@@ -10,7 +10,7 @@
 			<header>
 				<hgroup>
 					<h2 epub:type="ordinal z3998:roman">I</h2>
-					<h3 epub:type="title">Observations on the Causes of War</h3>
+					<p epub:type="title">Observations on the Causes of War</p>
 				</hgroup>
 				<blockquote epub:type="epigraph z3998:verse" xml:lang="la">
 					<p>

src/epub/text/chapter-2.xhtml

@@ -9,7 +9,7 @@
 		<section id="chapter-2" epub:type="chapter">
 			<hgroup>
 				<h2 epub:type="ordinal z3998:roman">II</h2>
-				<h3 epub:type="title">An Inquiry, <abbr>etc.</abbr></h3>
+				<p epub:type="title">An Inquiry, <abbr>etc.</abbr></p>
 			</hgroup>
 			<p>When I endeavor to divest myself of the influence of habit, and to contemplate a battle with those emotions which it would excite in the mind of a being who had never before heard of human slaughter, I find that I am impressed only with horror and astonishment; and perhaps, of the two emotions, astonishment is the greater.</p>
 			<p>That several thousand persons should meet together, and then deliberately begin to kill one another, appears to the understanding a proceeding so preposterous, so monstrous, that I think a being such as I have supposed, would inevitably conclude that they were mad. Nor, if it were attempted to explain to him some motives to such conduct, do I believe that he would be able to comprehend how any possible circumstances could make it reasonable. The ferocity and prodigious folly of the act would outbalance the weight of every conceivable motive, and he would turn, unsatisfied, away,</p>

src/epub/text/chapter-3.xhtml

@@ -10,7 +10,7 @@
 			<header>
 				<hgroup>
 					<h2 epub:type="ordinal z3998:roman">III</h2>
-					<h3 epub:type="title">Observations on the Effects of War</h3>
+					<p epub:type="title">Observations on the Effects of War</p>
 				</hgroup>
 				<blockquote epub:type="epigraph z3998:verse">
 					<p>

src/epub/text/halftitlepage.xhtml

@@ -9,7 +9,7 @@
 		<section id="halftitlepage" epub:type="halftitlepage">
 			<hgroup epub:type="fulltitle">
 				<h2 epub:type="title">An Inquiry Into the Accordancy of War with the Principles of Christianity</h2>
-				<h3 epub:type="subtitle">And an Examination of the Philosophical Reasoning by Which It Is Defended, with Observations on Some of the Causes of War and on Some of Its Effects</h3>
+				<p epub:type="subtitle">And an Examination of the Philosophical Reasoning by Which It Is Defended, with Observations on Some of the Causes of War and on Some of Its Effects</p>
 			</hgroup>
 		</section>
 	</body>