command alias parsing breaks parse_or_exit

[nerditation]

I have some utility using parse_or_exit for quick prototyping. after updating from 0.3.1 to 0.3.2, the macro fails to parse.

for example, the code and error message:

// error: invalid flags syntax, expected one of `optional`, `required`, `repeated`, got Some(Punct { ch: ':', spacing: Alone, span: #0 bytes(598..599) })
let flags = parse_or_exit! {
    required --name name: String
};

// this compiles, but the generated `Flags` type is empty:
let flags = parse_or_exit! {
    required --name
};

after some digging, I think it is due to all the Ident tokens (required, --name and name in the above example) are parsed and consumed as aliases by line 85:

xflags/crates/xflags-macros/src/parse.rs

Lines 77 to 85 in bc37dc0

	fn cmd_impl(p: &mut Parser, anon: bool) -> Result<ast::Cmd> {
	let name = if anon {
	String::new()
	} else {
	p.expect_keyword("cmd")?;
	cmd_name(p)?
	};
	let aliases = alias_names(p);

I made a local patch to put the alias parsing under the anon conditional guard, and it seems to have fixed the issue, as least for my simple use case:

	let (name, aliases) = if anon {
		(String::new(), vec![])
	} else {
		p.expect_keyword("cmd")?;
		(cmd_name(p)?, alias_names(p))
	};