Add options to remove descriptive elements (#102)

* --remove-titles (removes <title>)
* --remove-descriptions (removes <desc>)
* --remove-descriptive-elements (removes <title>, <desc> and <metadata>)

unittests/full-descriptive-elements.svg

@@ -0,0 +1,31 @@
+<svg xmlns="http://www.w3.org/2000/svg">
+    <title xmlns:mytitle="http://example.org/mytitle">
+      <mytitle:title>This is an example SVG file</mytitle:title>
+      <mytitle:desc>Unit test for Scour's --remove-titles option</mytitle:desc>
+    </title>
+    <desc xmlns:mydesc="http://example.org/mydesc">
+      <mydesc:title>This is an example SVG file</mydesc:title>
+      <mydesc:para>Unit test for Scour's
+      <mydesc:emph>--remove-descriptions</mydesc:emph> option</mydesc:para>
+    </desc>
+    <metadata>
+      <rdf:RDF
+           xmlns:rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+           xmlns:rdfs = "http://www.w3.org/2000/01/rdf-schema#"
+           xmlns:dc = "http://purl.org/dc/elements/1.1/" >
+        <rdf:Description about="http://example.org/myfoo"
+             dc:title="MyFoo"
+             dc:description="Unit test for Scour's --remove-metadata option"
+             dc:publisher="No One"
+             dc:date="2010-06-09"
+             dc:format="image/svg+xml"
+             dc:language="en" >
+          <dc:creator>
+            <rdf:Bag>
+              <rdf:li>No One</rdf:li>
+            </rdf:Bag>
+          </dc:creator>
+        </rdf:Description>
+      </rdf:RDF>
+    </metadata>
+</svg>