Add the Caplinger paper.

It seems this was the first conservative scanning GC.

Author: ltratt

softdev.bib

@@ -2871,3 +2871,12 @@ @inproceedings{craciunas08compacting
     month = Jun,
     year = 2008,
 }
+
+@inproceedings{caplinger88memory,
+  author = "Michael A. Caplinger",
+  title = "A Memory Allocator with Garbage Collection for {C}",
+  booktitle = "{USENIX}",
+  month = Jan,
+  year = 1998,
+  pages = "325--330",
+}