Add ability to configure timeoutThreshold

By default, the timeout threshold for Spymemcached is set to 998, which means
that each connection will wait for 998 timeouts before considering the connection
to be dead and then re-establishing a new one.

This changeset adds the ability to configure the threshold from Shade.

Also, bump Spymemcached version to the latest one.

build.sbt

@@ -62,7 +62,7 @@ resolvers ++= Seq(
 )
 
 libraryDependencies ++= Seq(
-  "net.spy"        %  "spymemcached"    % "2.12.2",
+  "net.spy"        %  "spymemcached"    % "2.12.3",
   "org.slf4j"      %  "slf4j-api"       % "1.7.23",
   "io.monix"       %% "monix-eval"      % "2.3.0",
   "ch.qos.logback" %  "logback-classic" % "1.1.7"  % Test,

src/main/scala/shade/memcached/Configuration.scala

@@ -38,6 +38,11 @@ import scala.concurrent.duration._
  * @param operationTimeout  is the default operation timeout; When the limit is reached, the
  *                          Future responses finish with Failure(TimeoutException)
  *
+ * @param timeoutThreshold  is the maximum number of timeouts for a connection that will be tolerated before
+ *                          the connection is considered dead and will not be retried. Once this threshold is breached,
+ *                          the client will consider the connection to be lost and attempt to establish a new one.
+ *                          If None, the default Spymemcached implementation is used (998)
+ *
  * @param shouldOptimize    If true, optimization will collapse multiple sequential get ops.
  *
  * @param opQueueFactory    can be used to customize the operations queue,
@@ -63,6 +68,7 @@ case class Configuration(
   protocol: Protocol.Value = Protocol.Binary,
   failureMode: FailureMode.Value = FailureMode.Retry,
   operationTimeout: FiniteDuration = 1.second,
+  timeoutThreshold: Option[Int] = None,
   shouldOptimize: Boolean = false,
   opQueueFactory: Option[OperationQueueFactory] = None,
   writeQueueFactory: Option[OperationQueueFactory] = None,

src/main/scala/shade/memcached/MemcachedImpl.scala

@@ -359,16 +359,21 @@ class MemcachedImpl(config: Configuration, ec: ExecutionContext) extends Memcach
           builder
       }
 
+      val withTimeoutThreshold = config.timeoutThreshold match {
+        case Some(threshold) => withTimeout.setTimeoutExceptionThreshold(threshold)
+        case _ => withTimeout
+      }
+
       val withAuth = config.authentication match {
         case Some(credentials) =>
-          withTimeout.setAuthDescriptor(
+          withTimeoutThreshold.setAuthDescriptor(
             new AuthDescriptor(
               Array("PLAIN"),
               new PlainCallbackHandler(credentials.username, credentials.password)
             )
           )
         case None =>
-          withTimeout
+          withTimeoutThreshold
       }
 
       withAuth