feat(Help): adds support for displaying info before help message

Can now use the `App::before_help` method to add additional information
that will be displayed prior to the help message. Common uses are
copyright, or license information.

src/app/help.rs

@@ -692,7 +692,8 @@ impl<'a> Help<'a> {
     ///     * `{options}`     - Help for options.
     ///     * `{positionals}` - Help for positionals arguments.
     ///     * `{subcommands}` - Help for subcommands.
-    ///     * `{after-help}`  - Help for flags.
+    ///     * `{after-help}`  - Info to be displayed after the help message.
+    ///     * `{before-help}` - Info to be displayed before the help message.
     ///
     /// The template system is, on purpose, very simple. Therefore the tags have to writen
     /// in the lowercase and without spacing.
@@ -768,6 +769,11 @@ impl<'a> Help<'a> {
                                 "{}",
                                 parser.meta.more_help.unwrap_or("unknown after-help")));
                 }
+                b"before-help" => {
+                    try!(write!(self.writer,
+                                "{}",
+                                parser.meta.pre_help.unwrap_or("unknown before-help")));
+                }
                 // Unknown tag, write it back.
                 ref r => {
                     try!(self.writer.write(b"{"));

src/app/meta.rs

@@ -7,6 +7,7 @@ pub struct AppMeta<'b> {
     pub version: Option<&'b str>,
     pub about: Option<&'b str>,
     pub more_help: Option<&'b str>,
+    pub pre_help: Option<&'b str>,
     pub usage_str: Option<&'b str>,
     pub usage: Option<String>,
     pub help_str: Option<&'b str>,
@@ -21,6 +22,7 @@ impl<'b> Default for AppMeta<'b> {
             author: None,
             about: None,
             more_help: None,
+            pre_help: None,
             version: None,
             usage_str: None,
             usage: None,
@@ -49,6 +51,7 @@ impl<'b> Clone for AppMeta<'b> {
             author: self.author,
             about: self.about,
             more_help: self.more_help,
+            pre_help: self.pre_help,
             version: self.version,
             usage_str: self.usage_str,
             usage: self.usage.clone(),

src/app/mod.rs

@@ -189,6 +189,23 @@ impl<'a, 'b> App<'a, 'b> {
         self
     }
 
+    /// Adds additional help information to be displayed in addition to auto-generated help. This
+    /// information is displayed **before** the auto-generated help information. This is often used
+    /// for header information.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// # use clap::App;
+    /// App::new("myprog")
+    ///     .before_help("Some info I'd like to appear before the help info")
+    /// # ;
+    /// ```
+    pub fn before_help<S: Into<&'b str>>(mut self, help: S) -> Self {
+        self.p.meta.pre_help = Some(help.into());
+        self
+    }
+
     /// Sets a string of the version number to be displayed when displaying version or help
     /// information.
     ///