Re-add the "json" pkg-config file as a compatibility shim.
Also rename the json-c-uninstalled.pc file.
diff --git a/configure.in b/configure.in
index 032dc8d..5b2eea3 100644
--- a/configure.in
+++ b/configure.in
@@ -41,9 +41,10 @@
 
 AC_CONFIG_FILES([
 Makefile
+json.pc
 json-c.pc
 tests/Makefile
-json-uninstalled.pc
+json-c-uninstalled.pc
 ])
 
 AC_OUTPUT