Add missing method to get the zim metadata.

According to https://wiki.openzim.org/wiki/Metadata

include/reader.h

@@ -205,6 +205,13 @@ class Reader
    */
   string getDescription() const;
 
+  /**
+   * Get the long description of the zim file.
+   *
+   * @return The long description of the zim file as specifed in the zim metadata.
+   */
+  string getLongDescription() const;
+
   /**
    * Get the language of the zim file.
    *
@@ -212,6 +219,13 @@ class Reader
    */
   string getLanguage() const;
 
+  /**
+   * Get the license of the zim file.
+   *
+   * @return The license of the zim file as specified in the zim metadata.
+   */
+  string getLicense() const;
+
   /**
    * Get the tags of the zim file.
    *
@@ -219,6 +233,34 @@ class Reader
    */
   string getTags() const;
 
+  /**
+   * Get the relations of the zim file.
+   *
+   * @return The relation of the zim file as specified in the zim metadata.
+   */
+  string getRelation() const;
+
+  /**
+   * Get the flavour of the zim file.
+   *
+   * @return The flavour of the zim file as specified in the zim metadata.
+   */
+  string getFlavour() const;
+
+  /**
+   * Get the source of the zim file.
+   *
+   * @return The source of the zim file as specified in the zim metadata.
+   */
+  string getSource() const;
+
+  /**
+   * Get the scraper of the zim file.
+   *
+   * @return The scraper of the zim file as specified in the zim metadata.
+   */
+  string getScraper() const;
+
   /**
    * Get the origId of the zim file.
    *

src/reader.cpp

@@ -337,15 +337,45 @@ string Reader::getDescription() const
   return value;
 }
 
+string Reader::getLongDescription() const
+{
+  METATAG("LongDescription")
+}
+
 string Reader::getLanguage() const
 {
   METATAG("Language")
 }
 
+string Reader::getLicense() const
+{
+  METATAG("License")
+}
+
 string Reader::getTags() const
 {
   METATAG("Tags")
 }
+
+string Reader::getRelation() const
+{
+  METATAG("Relation")
+}
+
+string Reader::getFlavour() const
+{
+  METATAG("Flavour")
+}
+
+string Reader::getSource() const
+{
+  METATAG("Source")
+}
+
+string Reader::getScraper() const
+{
+  METATAG("Scraper")
+}
 #undef METATAG
 
 string Reader::getOrigId() const