Add pretty print file to build

Add cn-print.c to the list of source files
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index ceb0608..8193cc6 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -8,6 +8,7 @@
       cn-encoder.c
       cn-error.c
       cn-get.c
+      cn-print.c
 )
 
 if (use_context)