Thrift: docstring revamp step 1.

Summary:
Allow constants to be documented.
Now any "Definition" can be documented, so we can move the docstring stuff
up to a a higher node in the parse tree.

Reviewed By: mcslee

Test Plan:
Recompiled thrift.
Checked out DocTest.thrift and a few other thrifts.

Revert Plan: ok


git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@665200 13f79535-47bb-0310-9956-ffa450edef68
4 files changed