Added <lastBuildDate> everywhere (#29)

* Last Build Date

I think that the <lastBuildDate> tag is also needed. I'm not sure if this is the best way to implement it though...

* Fixed the typo (ddate)

* Added <lastBuildDate> to the articles feed

* Added <lastBuildDate> to the categories feed

* Added <lastBuildDate> to the link feed

* Yet another typo

feed.articles.xml

@@ -7,6 +7,7 @@
 		<description>{% if site.description %}{{ site.description | xml_escape }}{% endif %}</description>
 		<link>{{ site.url }}</link>
 		<atom:link href="{{ site.url }}/{{ page.path }}" rel="self" type="application/rss+xml" />
+		<lastBuildDate>{% for post in site.posts limit:1 %}{% unless post.link %}{{ post.date | date_to_rfc822 }}{% endunless %}{% endfor %}</lastBuildDate>
 		{% for post in site.posts %}
 			{% unless post.link %}
 			<item>

feed.category.xml

@@ -7,6 +7,7 @@
 		<description>Posts categorized as 'miscellaneous'</description>
 		<link>{{ site.url }}</link>
 		<atom:link href="{{ site.url }}/{{ page.path }}" rel="self" type="application/rss+xml" />
+		<lastBuildDate>{% for post in site.categories.miscellaneous limit:1 %}{{ post.date | date_to_rfc822 }}{% endfor %}</lastBuildDate>
 		{% for post in site.categories.miscellaneous limit:10 %}
 			<item>
 				<title>{{ post.title | xml_escape }}</title>

feed.links.xml

@@ -7,6 +7,7 @@
 		<description>{% if site.description %}{{ site.description | xml_escape }}{% endif %}</description>
 		<link>{{ site.url }}</link>
 		<atom:link href="{{ site.url }}/{{ page.path }}" rel="self" type="application/rss+xml" />
+		<lastBuildDate>{% for post in site.posts limit:1 %}{% if post.link %}{{ post.date | date_to_rfc822 }}{% ifunless %}{% endfor %}</lastBuildDate>
 		{% for post in site.posts %}
 			{% if post.link %}
 			<item>

feed.xml

@@ -7,6 +7,7 @@
 		<description>{% if site.description %}{{ site.description | xml_escape }}{% endif %}</description>		
 		<link>{{ site.url }}</link>
 		<atom:link href="{{ site.url }}/{{ page.path }}" rel="self" type="application/rss+xml" />
+		<lastBuildDate>{% for post in site.posts limit:1 %}{{ post.date | date_to_rfc822 }}{% endfor %}</lastBuildDate>
 		{% for post in site.posts limit:10 %}
 			<item>
 				<title>{{ post.title | xml_escape }}</title>