added information about keycharge in response to signing request

docs/api.md

@@ -159,6 +159,7 @@ If the key isn't charged enough for the amount of tokens or if the date supplied
 {
     "key": "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx",
     "discharged": <AMOUNT_THAT_WAS_DISCHARGED>,
+    "charge": <NEW_CHARGE_OF KEY>,
     "date": <DATE_AS_SUPPLIED_IN_TOKEN_PUBKEY>,
     "signed_tokens": {
         "<BLINDED_TOKEN_BIGINT_AS_STRING>": "<SIGNATURE_BIGINT_AS_STRING>",

pass/routes/api.js

@@ -246,6 +246,7 @@ router.post(
     res.status(201).json({
       key: key.get_key,
       discharged: blinded_tokens.length,
+      charge: key.get_charge(),
       date: date.format(config.get("crypto.private_key.date_format")),
       signed_tokens: signed_tokens,
     });