Port network/url command (#452)

* feat: add url command

* feat(network/url): add sub-command for url

crates/nu-command/src/lib.rs

@@ -10,6 +10,7 @@ mod filesystem;
 mod filters;
 mod formats;
 mod math;
+mod network;
 mod platform;
 mod random;
 mod shells;
@@ -29,6 +30,7 @@ pub use filesystem::*;
 pub use filters::*;
 pub use formats::*;
 pub use math::*;
+pub use network::*;
 pub use platform::*;
 pub use random::*;
 pub use shells::*;