Add BEJ tree API.

This API allows us to represent a JSON object with a linked list
representation.

Signed-off-by: Kasun Athukorala <kasunath@google.com>
Change-Id: I7894e7c10e4db2ad02a79b01bb4d7a48d5a197cd
diff --git a/test/meson.build b/test/meson.build
index 8178dc1..07807c4 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -19,6 +19,7 @@
   'bej_decoder',
   'bej_common',
   'bej_dictionary',
+  'bej_tree',
 ]
 foreach t : gtests
   test(t, executable(t.underscorify(), t + '_test.cpp',