Capitalize "positional" and "optional" in help message

It looks better (IMO) and it’s also consistent with "Usage" that is
already capitalized.

Author: jirutka

README.rst

@@ -63,7 +63,7 @@ what we have now::
 
     Greet somebody.
 
-    optional arguments:
+    Optional arguments:
      -h, --help  show this help message and exit
      -v, --verbose
                  Be verbose

src/parser.rs

@@ -897,7 +897,7 @@ impl<'a, 'b> HelpFormatter<'a, 'b> {
         if self.parser.arguments.len() > 0
             || self.parser.catchall_argument.is_some()
         {
-            try!(write!(self.buf, "\npositional arguments:\n"));
+            try!(write!(self.buf, "\nPositional arguments:\n"));
             for arg in self.parser.arguments.iter() {
                 try!(self.print_argument(&**arg));
             }
@@ -911,7 +911,7 @@ impl<'a, 'b> HelpFormatter<'a, 'b> {
         if self.parser.short_options.len() > 0
             || self.parser.long_options.len() > 0
         {
-            try!(write!(self.buf, "\noptional arguments:\n"));
+            try!(write!(self.buf, "\nOptional arguments:\n"));
             for opt in self.parser.options.iter() {
                 try!(self.print_option(&**opt));
             }

src/test_help.rs

@@ -14,7 +14,7 @@ fn test_empty() {
         + "\n"
         + "Test program\n"
         + "\n"
-        + "optional arguments:\n"
+        + "Optional arguments:\n"
         + "  -h,--help             show this help message and exit\n"
         , from_utf8(&buf[..]).unwrap().to_string());
 }
@@ -42,7 +42,7 @@ Test program. The description of the program is ought to be very long, because
 we want to test how word wrapping works for it. So some more text would be ok
 for the test\n"
         + "\n"
-        + "optional arguments:\n"
+        + "Optional arguments:\n"
         + "  -h,--help             show this help message and exit\n"
         + "  --value VALUE         Set integer value\n"
         + "  -L,--long-option LONG_OPTION\n"
@@ -65,10 +65,10 @@ fn test_argument() {
         + "\n"
         + "Test program\n"
         + "\n"
-        + "positional arguments:\n"
+        + "Positional arguments:\n"
         + "  value                 Integer value\n"
         + "\n"
-        + "optional arguments:\n"
+        + "Optional arguments:\n"
         + "  -h,--help             show this help message and exit\n"
         , from_utf8(&buf[..]).unwrap().to_string());
 }
@@ -92,11 +92,11 @@ fn test_arguments() {
         + "\n"
         + "Test program\n"
         + "\n"
-        + "positional arguments:\n"
+        + "Positional arguments:\n"
         + "  v1                    Integer value 1\n"
         + "  v2                    More values\n"
         + "\n"
-        + "optional arguments:\n"
+        + "Optional arguments:\n"
         + "  -h,--help             show this help message and exit\n"
         , from_utf8(&buf[..]).unwrap().to_string());
 }
@@ -122,11 +122,11 @@ fn test_req_arguments() {
         + "\n"
         + "Test program\n"
         + "\n"
-        + "positional arguments:\n"
+        + "Positional arguments:\n"
         + "  v1                    Integer value 1\n"
         + "  v2                    More values\n"
         + "\n"
-        + "optional arguments:\n"
+        + "Optional arguments:\n"
         + "  -h,--help             show this help message and exit\n"
         , from_utf8(&buf[..]).unwrap().to_string());
 }
@@ -147,7 +147,7 @@ fn test_metavar() {
         + "\n"
         + "Test program.\n"
         + "\n"
-        + "optional arguments:\n"
+        + "Optional arguments:\n"
         + "  -h,--help             show this help message and exit\n"
         + "  -L,--long-option VAL  Long option value\n"
         , from_utf8(&buf[..]).unwrap().to_string());