THRIFT-564. Support arbitrary annotations on struct fields

This is subtly different from a type annotation, since some bits of
metadata only make sense in the context of a single structure field,
like whether the field is required, or whether the C++ code should use
a pointer for it.

This change doesn't define any meaningful annotations.  It just sets up
the parsing infrastructure.

I have no idea if $10 will work with older versions of yacc.  It seems
to work fine with bison.

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@919325 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/test/AnnotationTest.thrift b/test/AnnotationTest.thrift
index ef9ba13..1a34320 100644
--- a/test/AnnotationTest.thrift
+++ b/test/AnnotationTest.thrift
@@ -20,8 +20,8 @@
 typedef list<i32> ( cpp.template = "std::list" ) int_linked_list
 
 struct foo {
-  1: i32 bar;
-  2: i32 baz;
+  1: i32 bar ( presence = "required" );
+  2: i32 baz ( presence = "manual", cpp.use_pointer = "", );
   3: i32 qux;
   4: i32 bop;
 } (