Handle the renaming of programs, services and structs.

[AlexisMontagne]

The thrift * namespace and service name has became a crucial part of our infrastructure as it is used in the service discovery process. We lost the ability to reshuffle/rename our interface repo.

This PR aims at providing a way to handle gracefully the change of namespace or service name.

This adds two directives to the thrift grammar

1 - previously_known_as

The entire program as been renamed

namespace * foo.v1.bar

previously_known_as foo.bar

service Buz {}

It means that our SD system will be called for foo.v1.bar.Buz first and if no match is found, foo.bar.Buz will be inquired

2 - @previously_known_as

Only a service or a struct has been moved

namespace * foo.v1.bar

service Baz {}

@previously_known_as{namespace="foo.bar",name="Buzz"}
service Buz {}

It allows finer grained control over the rewrite.