WIP: RFC 1 : Abstract Syntax Tree-based output script locks

Update 2 : Rewriting with way better format to fix flaws of the first draft.

In the current Duniter protocol input and output conditions are stored in machine-readable BNF text format. This is good for human readability, but it requires parsing and takes place due to its textual format.

To lower blocksize and transactions weights; or to allow more complex conditions, it could be preferable to use a more simple binary format which need little or no parsing, close to memory and that can be converted back to text format. It can also allow to add new features without hard-forking the protocol.

DIP0001.md

@@ -63,7 +63,7 @@ As seen in exemples above, we have to manage different types of tree nodes :
 - **Local values of different types** : leaf nodes with values stored in the script (like pubkeys)
 - **Extern values** : leaf nodes with values provided as input to the script (like signatures)
 
-We'll also need a valid way to not provide an ununsed input, and to provide the hash of an AST.
+We'll also need a valid way to not provide an ununsed/undefined input, and another one to provide the hash of an AST.
 
 We can define opcodes to encode this information :
 
@@ -160,9 +160,10 @@ Input parameters are provided in a list of AST with indexes.
 In the exemple of 2 out of 3 signatures above, the input could be :
 
 ```
-0 : U64 <signature_a>
-1 : NOP
-2 : U64 <signature_b>
+3
+    U64 <signature_a>
+    NOP
+    U64 <signature_c>
 ```
 
 In the document, they will be expressed as `<size on 2 bytes> <ast1> <ast2> ...`.
@@ -203,7 +204,7 @@ pubkey   signature
 
 If the left signature verification returns true, the `OR` operator returns true. Otherwise it will propagate the **undefined state**.
 
-At the end the response is `UNDEFINED`. For a calculating node, this transaction is invalid. For a mirror node, it can consider it valid if it comes from a calculating node. Further verifications may be necessary.
+If at the end the returned value is `UNDEFINED`, the execution is concidered invalid and the transaction can't be spent.
 
 # Merklized trees
 
@@ -244,10 +245,11 @@ SMR 2
 Then when you want to use it, you provide as parameters :
 
 ```
-0 : U64 <signature_a>
-1 : NOP
-2 : U64 <signature_c>
-3 : GE 2
+4
+    U64 <signature_a>
+    NOP
+    U64 <signature_c>
+    GE 2
         SUM 3
             ED 2
                 U32 <public_key_a>