fixing output indentation

Taking the output formatting forward I made this:

```html
<!DOCTYPE html>
<html>
	<head>
		<title>Hello, World!</title>
	</head>
	<body>
		<header>
			<h1>
	Page title line 1
	Page title line 2
</h1>
<h2>
	<span>Subtitle line 1</span>
<span>Subtitle line 2</span>
</h2>
		</header>
		<section>
			<div>
	<p>Page content line 1</p>
<p>Page content line 2</p>
</div>
		</section>
		<section>
			redefined side1 content line1
redefined side1 content line2
		</section>
		<section>
			side2 content line 1
side2 content line 2
		</section>
		<footer>
			<p>Footer content 1</p>
<p>Footer content 2</p>
		</footer>
	</body>
</html>
```

into this:

```html
<!DOCTYPE html>
<html>
	<head>
		<title>Hello, World!</title>
	</head>
	<body>
		<header>
			<h1>
				Page title line 1
				Page title line 2
			</h1>
			<h2>
				<span>Subtitle line 1</span>
				<span>Subtitle line 2</span>
			</h2>
		</header>
		<section>
			<div>
				<p>Page content line 1</p>
				<p>Page content line 2</p>
			</div>
		</section>
		<section>
			redefined side1 content line1
			redefined side1 content line2
		</section>
		<section>
			side2 content line 1
			side2 content line 2
		</section>
		<footer>
			<p>Footer content 1</p>
			<p>Footer content 2</p>
		</footer>
	</body>
</html>
```

It works by prefixing each line in every `include`'s and `content`'s content with the original tag's indentation. This way one can author all the partials with 0 initial indentation and every command tag can be placed correctly in the document flow.