THRIFT-2824

https://issues.apache.org/jira/browse/THRIFT-2824

We use the html generator to create and publish documentation for our services. We primarily use the program level doctext to insert html documentation for the entire service.
We would like to add richer content up top, but are limited by the escaping performed by the html generator on doctexts.
This patch adds the "noescape" flag to simply render doctexts as-is.