Server-sent-event fixes

This makes several changes to server-sent events to allow it to merge
to master.  The routing system has been removed in leiu of using
content-type eventstream detection.  Timers have been added to the
sse connections, and sse connections now rely on async_wait, rather
than a full read.

Tested: WIP

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: Id0ff0ebc2b3a795b3dba008e440556a9fdd882c2
diff --git a/include/http_utility.hpp b/include/http_utility.hpp
index 8f2478f..d18ac4b 100644
--- a/include/http_utility.hpp
+++ b/include/http_utility.hpp
@@ -26,6 +26,7 @@
     HTML,
     JSON,
     OctetStream,
+    EventStream,
 };
 
 struct ContentTypePair
@@ -34,11 +35,12 @@
     ContentType contentTypeEnum;
 };
 
-constexpr std::array<ContentTypePair, 4> contentTypes{{
+constexpr std::array<ContentTypePair, 5> contentTypes{{
     {"application/cbor", ContentType::CBOR},
     {"application/json", ContentType::JSON},
     {"application/octet-stream", ContentType::OctetStream},
     {"text/html", ContentType::HTML},
+    {"text/event-stream", ContentType::EventStream},
 }};
 
 inline ContentType