Tchannel

-------------------

- Made "service" optional for ``thrift.load()``. The first argument should be a
path, but backwards compatibility is provided for 0.17.0.

-------------------

- It is now possible to load Thrift IDL files directly with
``tchannel.thrift.load``. This means that the code generation step using the
Apache Thrift compiler can be skipped entirely. Check the API documentation
for more details.
- Accept host file in advertise: ``TChannel.advertise()`` now accepts
a parameter, ``router_file`` that contains a JSON stringified format
of the router list.
- Add ``TChannel.is_listening`` method to return whether the tchannel instance
is listening or not.

--------------------

- Fix default timeout incorrectly set to 16 minutes, now 30 seconds.

-------------------

- Network failures while connecting to randomly selected hosts should be
retried with other hosts.

-------------------

- Revert timeout changes from 0.16.7 due to client incompatibilities.

-------------------

- Fixed an issue where timeouts were being incorrectly converted to seconds.