Support for multiple positionals of different type

[aherrmann]

#97 (comment)

For example <u32> <string>... will make the positionals field in the result be []const u32, ignoring that the other positional parameter specified string.

[michidk]

I thought this meant, that I can specify it as <u16> in the help and then parse the []const u32 into a u16 by hand.

But it actually does not even compile.
This:

    const params = comptime clap.parseParamsComptime(
        \\-h, --help                   Display this help.
        \\<str>                     	The host to connect to.
        \\<u16>                     	The port to connect to.
        \\
    );

, gives the following error:

vscode ➜ /workspaces/my-project (main) $ zig build
zig build-exe my-project Debug native: error: the following command failed with 1 compilation errors:
/usr/local/lib/zig/zig build-exe /workspaces/my-project/src/main.zig --cache-dir /workspaces/my-project/zig-cache --global-cache-dir /home/vscode/.cache/zig --name my-project --mod clap::/home/vscode/.cache/zig/p/1220f48518ce22882e102255ed3bcdb7aeeb4891f50b2cdd3bd74b5b2e24d3149ba2/clap.zig --deps clap --listen=- 
Build Summary: 0/5 steps succeeded; 1 failed (disable with --summary none)
run transitive failure
└─ run my-project transitive failure
   ├─ zig build-exe my-project Debug native 1 errors
   └─ install transitive failure
      └─ install my-project transitive failure
         └─ zig build-exe my-project Debug native (reused)
/home/vscode/.cache/zig/p/1220f48518ce22882e102255ed3bcdb7aeeb4891f50b2cdd3bd74b5b2e24d3149ba2/clap.zig:813:47: error: expected type '[]const u8', found 'u16'
        .positional => try positionals.append(try parser(arg.value.?)),
                                              ^~~~~~~~~~~~~~~~~~~~~~~
/usr/local/lib/zig/lib/std/array_list.zig:206:42: note: parameter type declared here
        pub fn append(self: *Self, item: T) Allocator.Error!void {

So the only way I can make this work is by using <str> for both.