Add source code.

include/CommandSpec.h

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <cstddef>
+#include <string>
+#include <vector>
+
+// What kind of value an argument holds (drives tab completion).
+enum class ArgKind {
+    None,
+    Task,
+    Account,
+    AccountOrDash,
+    AccountOrStatus,
+    Status,
+    Visibility,
+    TaskLevel,
+    AccountLevel,
+    File,
+    Editor
+};
+
+struct CommandSpec {
+    std::string key;    // e.g. "tsk add"
+    std::string usage;  // e.g. "tsk add <name> [acc] [status]"
+    std::string help;
+    std::size_t minArgs = 0;
+    std::size_t maxArgs = 0;
+    std::vector<ArgKind> argKinds;
+};