refactor: one error code file (#161)

error_codes.md

@@ -0,0 +1,32 @@
+# NUT Errors
+
+| Code  | Description                                     | Relevant nuts                            |
+| ----- | ----------------------------------------------- | ---------------------------------------- |
+| 10002 | Blinded message of output already signed        | [NUT-03][03], [NUT-04][04], [NUT-05][05] |
+| 10003 | Token could not be verified                     | [NUT-03][03], [NUT-05][05]               |
+| 11001 | Token is already spent                          | [NUT-03][03], [NUT-05][05]               |
+| 11002 | Transaction is not balanced (inputs != outputs) | [NUT-02][02], [NUT-03][03], [NUT-05][05] |
+| 11005 | Unit in request is not supported                | [NUT-04][04], [NUT-05][05]               |
+| 11006 | Amount outside of limit range                   | [NUT-04][04], [NUT-06][06]               |
+| 12001 | Keyset is not known                             | [NUT-02][02], [NUT-04][04]               |
+| 12002 | Keyset is inactive, cannot sign messages        | [NUT-02][02], [NUT-03][03], [NUT-04][04] |
+| 20001 | Quote request is not paid                       | [NUT-04][04]                             |
+| 20002 | Tokens have already been issued for quote       | [NUT-04][04]                             |
+| 20003 | Minting is disabled                             | [NUT-04][04]                             |
+| 20005 | Quote is pending                                | [NUT-04][04], [NUT-05][05]               |
+| 20006 | Invoice already paid                            | [NUT-05][05]                             |
+| 20007 | Quote is expired                                | [NUT-04][04], [NUT-05][05]               |
+
+[00]: 00.md
+[01]: 01.md
+[02]: 02.md
+[03]: 03.md
+[04]: 04.md
+[05]: 05.md
+[06]: 06.md
+[07]: 07.md
+[08]: 08.md
+[09]: 09.md
+[10]: 10.md
+[11]: 11.md
+[12]: 12.md