Add a requirements.txt parser

crates/puffin-cli/src/commands/mod.rs

@@ -0,0 +1,30 @@
+use std::process::ExitCode;
+
+pub(crate) use install::install;
+
+mod install;
+
+#[derive(Copy, Clone)]
+pub(crate) enum ExitStatus {
+    /// The command succeeded.
+    #[allow(unused)]
+    Success,
+
+    /// The command failed due to an error in the user input.
+    #[allow(unused)]
+    Failure,
+
+    /// The command failed with an unexpected error.
+    #[allow(unused)]
+    Error,
+}
+
+impl From<ExitStatus> for ExitCode {
+    fn from(status: ExitStatus) -> Self {
+        match status {
+            ExitStatus::Success => ExitCode::from(0),
+            ExitStatus::Failure => ExitCode::from(1),
+            ExitStatus::Error => ExitCode::from(2),
+        }
+    }
+}