Merge pull request #50 from tomaka/close-46

Make `chainHead_unstable_unpin` accept multiple block hashes at once

Author: josepot

src/api/chainHead_unstable_unpin.md

@@ -3,7 +3,7 @@
 **Parameters**:
 
 - `followSubscription`: An opaque string that was returned by `chainHead_unstable_follow`.
-- `hash`: String containing the hexadecimal-encoded hash of the header of the block to unpin.
+- `hash`: String or array of strings containing the hexadecimal-encoded hash of the header of the block to unpin.
 
 **Return value**: *null*
 
@@ -13,8 +13,10 @@ On-going calls to `chainHead_unstable_body`, `chainHead_unstable_call` and `chai
 
 Has no effect if the `followSubscription` is invalid or stale.
 
+If this function returns an error, then no block must have been unpinned. Implementations are expected to start unpinning the blocks only after it has made sure that all the blocks could be unpinned.
+
 ## Possible errors
 
-- A JSON-RPC error is generated if the `followSubscription` is valid but the block hash passed as parameter doesn't correspond to any block that has been reported by `chainHead_unstable_follow`.
-- A JSON-RPC error is generated if the `followSubscription` is valid but the block hash passed as parameter has already been unpinned.
+- A JSON-RPC error is generated if the `followSubscription` is valid but at least one of the block hashes passed as parameter doesn't correspond to any block that has been reported by `chainHead_unstable_follow`.
+- A JSON-RPC error is generated if the `followSubscription` is valid but at least one of the the block hashes passed as parameter has already been unpinned.
 - No error is generated if the `followSubscription` is invalid or stale. The call is simply ignored.