External subcommands are now supported via the following:
```rust
extern crate clap;
use clap::{App, AppSettings};
fn main() {
// Assume there is a third party subcommand named myprog-subcmd
let m = App::new("myprog")
.setting(AppSettings::AllowExternalSubcommands)
.get_matches_from(vec![
"myprog", "subcmd", "--option", "value", "-fff", "--flag"
]);
// All trailing arguments will be stored under the subcommands sub-matches under a
// value of their runtime name (in this case "subcmd")
match m.subcommand() {
(external, Some(ext_m)) => {
let ext_args: Vec<&str> = ext_m.values_of(external).unwrap().collect();
assert_eq!(ext_args ,["--option", "value", "-fff", "--flag"]);
},
_ => unreachable!()
}
}
```
Closes#372
By using AppSettings::AllowLeadingHyphen values starting with a
leading hyphen (such as a negative number) are supported. This
setting should be used with caution as it silences certain
circumstances which would otherwise be an error (like forgetting
a value to an option argument).
Closes#385
