gitignore *.{cc,hh}, whitelist library/*.{cc,hh}

ttcn3 creates these files, and they clutter 'git status' output.

Change-Id: I6b7868ae71d3d3e710232b22a964f701ae8bd05d
diff --git a/.gitignore b/.gitignore
index cc06c3c..6973828 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,8 +1,10 @@
-bin/*.cc
-bin/*.hh
 deps/*/
 *.o
 *.log
 *.so
 compile
 */.gitignore
+*.cc
+*.hh
+!library/*.cc
+!library/*.hh