Added SubCommand examples

examples/08_SubCommands.rs

@@ -0,0 +1,57 @@
+extern crate clap;
+
+use clap::{App, Arg, SubCommand};
+
+fn main() {
+
+	// SubCommands function exactly like sub-Apps, because that's exactly what they are. Each
+	// instance of a SubCommand can have it's own version, author(s), Args, and even it's own
+	// subcommands.
+	//
+	// # Help and Version
+	// Just like Apps, each subcommand will get it's own "help" and "version" flags automatically
+	// generated. Also, like Apps, you can override "-v" or "-h" safely and still get "--help" and
+	// "--version" auto generated.
+	//
+	// NOTE: If you specify a subcommand for your App, clap will also autogenerate a "help" 
+	// subcommand along with "-h" and "--help" (applies to sub-subcommands as well).
+	//
+	// Just like arg() and args(), subcommands can be specified one at a time via subcommand() or
+	// multiple ones at once with a Vec<SubCommand> provided to subcommands(). 
+    let matches = App::new("MyApp")
+    					// Normal App and Arg configuration goes here...
+
+    					// In the following example assume we wanted an application which
+    					// supported an "add" subcommand, this "add" subcommand also took
+    					// one positional argument of a file to add:
+    					.subcommand(SubCommand::new("add")								// The name we call argument with 
+    											.about("Adds files to myapp")		    // The message displayed in "myapp -h"
+    																					// or "myapp help"
+    											.version("0.1")							// Subcommands can have independant version
+    											.author("Kevin K.")						// And authors
+    											.arg(Arg::new("input")					// And their own arguments
+    														.help("the file to add")
+    														.index(1)
+    														.required(true)))
+                        .get_matches();
+
+    // You can check if a subcommand was used like normal
+    if matches.is_present("add") {
+    	println!("'myapp add' was run.");
+    }
+    
+    // You can get the independant subcommand matches (which function exactly like App matches)
+    if let Some(ref matches) = matches.subcommand_matches("add") {
+    	// Safe to use unwrap() becasue of the required() option
+    	println!("Adding file: {}", matches.value_of("input").unwrap());
+    }
+
+    // You can also match on a subcommand's name
+    match matches.subcommand_name() {
+    	Some("add") => println!("'myapp add' was used"),
+    	None        => println!("No subcommand was used"),
+    	_			=> println!("Some other subcommand was used"),
+    }
+    
+    // Continued program logic goes here...
+}