feat: add simple check command

examples/syntax.ak

@@ -0,0 +1,17 @@
+use aiken/context.{ScriptContext}
+
+pub type Datum {
+  something: String,
+}
+
+pub type Redeemer {
+  Buy
+  Sell
+}
+
+pub fn validate(datum: Datum, rdmr: Redeemer, ctx: ScriptContext) -> Bool {
+  when rdmr is {
+    Buy -> True
+    Sell -> datum.something == "Aiken"
+  }
+}