_s: Add custom taxonomy support for term descriptions in taxonomy

archives.

We don't even have to check for a context before printing the
description, `term_description()` does all the heavy lifting for us.

Props @jasondpx. Fixes #128.

archive.php

@@ -66,20 +66,10 @@
 					?>
 				</h1>
 				<?php
-					if ( is_category() ) :
-						// show an optional category description
-						$category_description = category_description();
-						if ( ! empty( $category_description ) ) :
-							echo apply_filters( 'category_archive_meta', '<div class="taxonomy-description">' . $category_description . '</div>' );
-						endif;
-
-					elseif ( is_tag() ) :
-						// show an optional tag description
-						$tag_description = tag_description();
-						if ( ! empty( $tag_description ) ) :
-							echo apply_filters( 'tag_archive_meta', '<div class="taxonomy-description">' . $tag_description . '</div>' );
-						endif;
-
+					// Show an optional term description.
+					$term_description = term_description();
+					if ( ! empty( $term_description ) ) :
+						printf( '<div class="taxonomy-description">%s</div>', $term_description );
 					endif;
 				?>
 			</header><!-- .page-header -->