util: add "in order" mode to SegmentFetcher

This commit adds an option for the fetcher to emit a signal when a segment
has arrived in order. Out-of-order segments are maintained internally by
the fetcher and are deleted when the signal is emitted.

Change-Id: I84aec680774af3e3c07bb07c881eab8908b5c9c2
diff --git a/AUTHORS.md b/AUTHORS.md
index 261d9b6..13919c0 100644
--- a/AUTHORS.md
+++ b/AUTHORS.md
@@ -10,6 +10,7 @@
 * Hila Ben Abraham <https://sites.wustl.edu/hbabraham>
 * Shuo Chen <https://github.com/chenatu>
 * Muktadir R. Chowdhury <https://github.com/alvyC>
+* Jeremy Clark <https://github.com/jrandallclark>
 * Damian Coomes <https://github.com/dmcoomes>
 * Stephanie DiBenedetto
 * Qiuhan Ding <https://irl.cs.ucla.edu/~qiuhanding>