Support for semicolon comment delimiter

doc/overview.xml

@@ -500,6 +500,9 @@ notify(vm);
         <listitem><para>The <literal>#</literal> character introduces a
         comment that spans until the end of the line.</para>
         </listitem>
+        <listitem><para>The <literal>;</literal> character at the beginning of
+        a line makes the entire line a comment.</para>
+        </listitem>
       </itemizedlist>
 
       <para>The option names are relative to the section names, so

src/config_file.cpp

@@ -90,7 +90,13 @@ namespace boost { namespace program_options { namespace detail {
             // strip '#' comments and whitespace
             if ((n = s.find('#')) != string::npos)
                 s = s.substr(0, n);
-            s = trim_ws(s);
+            // if the first character is a ';' line is a comment
+            if (!s.empty() && ';' == *s.begin()) {
+                s = "";
+            }
+            else {
+                s = trim_ws(s);
+            }
 
             if (!s.empty()) {
                 // Handle section name

test/parsers_test.cpp

@@ -267,6 +267,7 @@ void test_config_file(const char* config_file)
 
     const char content1[] =
     " gv1 = 0#asd\n"
+    "; semi comment\n"
     "empty_value = \n"
     "plug3 = 7\n"
     "b = true\n"