Reorganize spec evaluation

src/eval/command/birthday.rs

@@ -0,0 +1,10 @@
+use crate::files::commands::BirthdaySpec;
+
+use super::super::command::CommandState;
+use super::super::Result;
+
+impl<'a> CommandState<'a> {
+    pub fn eval_birthday_spec(&mut self, spec: &BirthdaySpec) -> Result<()> {
+        todo!()
+    }
+}