Draft a few more core types for ScriptContext / Transaction

Interesting points:

  - We don't have tuples yet, so we fake it until we make it.
  - Aliases are 'order-sensitive', especially if an alias uses another not-yet-declared alias.

examples/aiken_std/lib/aiken/context.ak

@@ -4,14 +4,44 @@ pub type ScriptContext(purpose) {
 }
 
 pub type Transaction {
-  inputs: List(Nil),
+  inputs: List(Input),
+  reference_inputs: List(Input),
   outputs: List(Nil),
-  fee: Nil,
+  fee: Value,
-  mint: Nil,
+  mint: Value,
   certificates: List(Nil),
   withdrawals: List(Nil),
   validity_range: Nil,
   extra_signatories: Nil,
+  redeemers: List(Nil),
   datums: List(Nil),
-  id: ByteArray,
+  id: TransactionId,
 }
+
+pub type TransactionId =
+  ByteArray
+
+pub type Input {
+  output_reference: OutputReference,
+  output: Output,
+}
+
+pub type OutputReference {
+  transction_id: TransactionId,
+  output_index: Int,
+}
+
+pub type PolicyId =
+  ByteArray
+
+pub type Output =
+  Nil
+
+pub type AssetName =
+  ByteArray
+
+pub type Pair(a, b) =
+  Nil
+
+pub type Value =
+  List(Pair(PolicyId, List(Pair(AssetName, Int))))