enable "--threads:on" for tests (#75)

* enable "--threads:on" for tests

* disable Chronicles colours on Windows

* delete forLoopMacros-related config

beacon_chain/gossipsub_protocol.nim

@@ -55,6 +55,7 @@ p2pProtocol GossipSub(version = 1,
         p.state.sentMessages.incl msgId
         asyncCheck p.emit(topic, msgId, msg)
 
+    {.gcsafe.}:
       let handler = peer.networkState.topicSubscribers.getOrDefault(topic)
       if handler != nil:
         await handler(msg)

nim.cfg

@@ -1,5 +1,5 @@
-# https://github.com/nim-lang/Nim/issues/8691#issuecomment-414662209
-# Doesn't work unfortunately
-@if nimHasForLoopMacros:
---experimental:forLoopMacros
+# https://github.com/nim-lang/Nim/issues/8294#issuecomment-454556051
+@if windows:
+  -d:"chronicles_colors=NoColors"
 @end
+

tests/nim.cfg

@@ -0,0 +1,2 @@
+--threads:on
+