refactor: give every command we run a type of its own

src/cmd/django.rs

@@ -0,0 +1,44 @@
+use super::{Argv, Cmd};
+
+// an interactive shell in the django container
+pub struct Bash;
+
+impl Cmd for Bash {
+    fn argv(&self) -> Argv {
+        Argv::new("bash")
+    }
+}
+
+// django's manage.py, with the subcommand and its arguments
+pub struct Manage<'a> {
+    args: &'a [String],
+}
+
+impl<'a> Manage<'a> {
+    pub fn new(args: &'a [String]) -> Self {
+        Self { args }
+    }
+}
+
+impl Cmd for Manage<'_> {
+    fn argv(&self) -> Argv {
+        Argv::new("python").arg("manage.py").args(self.args)
+    }
+}
+
+// whatever the caller typed, passed through as it stands
+pub struct Words<'a> {
+    words: &'a [String],
+}
+
+impl<'a> Words<'a> {
+    pub fn new(words: &'a [String]) -> Self {
+        Self { words }
+    }
+}
+
+impl Cmd for Words<'_> {
+    fn argv(&self) -> Argv {
+        Argv::default().args(self.words)
+    }
+}