updated docs

docs/docs/optimization.xml

@@ -545,7 +545,7 @@ However, for graphs with cycles, the solution may be approximate.
          <file>dlib/optimization.h</file>
          <spec_file link="true">dlib/optimization/find_max_parse_cky_abstract.h</spec_file>
          <description>
-            This is a pair of functions useful for converting a parse tree output by 
+            This is a set of functions useful for converting a parse tree output by 
             <a href="#find_max_parse_cky">find_max_parse_cky</a> into a bracketed string
             suitable for displaying the parse tree.  
          </description>

docs/docs/term_index.xml

@@ -86,6 +86,8 @@
          <term file="optimization.html" name="parse_tree_to_string"/>
          <term file="optimization.html" name="find_trees_not_rooted_with_tag"/>
          <term link="optimization.html#parse_tree_to_string" name="parse_tree_to_string_tagged"/>
+         <term link="optimization.html#parse_tree_to_string" name="parse_trees_to_string"/>
+         <term link="optimization.html#parse_tree_to_string" name="parse_trees_to_string_tagged"/>
          <term file="dlib/optimization/find_max_parse_cky_abstract.h.html" name="parse_tree_to_string_error"/>
          <term file="dlib/optimization/find_max_parse_cky_abstract.h.html" name="constituent"/>
          <term file="dlib/optimization/find_max_parse_cky_abstract.h.html" name="parse_tree_element"/>