Jupyterhub

This release is compatible with JupyterHub 0.5.0 through 0.8.1/0.9dev.

- SlurmSpawner: Remove `--uid` for (at least) Slurm 17.11 compatibility. If you use `sudo`, this should not be necessary, but because this is security related you should check that user management is as you expect. If your configuration does not use `sudo` then you may need to add the `--uid` option in a custom `batch_script`.
- add base options `req_ngpus` `req_partition` `req_account` and `req_options`
- Fix up logging
- Merge `user_options` with the template substitution vars instead of having it as a separate key
- Update ip/port handling for JupyterHub 0.8
- Add `LICENSE` (BSD3) and `CONTRIBUTING.md`
- Add `LsfSpawner` for IBM LFS
- Add `MultiSlurmSpawner`
- Add `MoabSpawner`
- Add `condorSpawner`
- Add `GridEngineSpawner`
- SlurmSpawner: add `req_qos` option
- WrapSpawner and ProfilesSpawner, which provide mechanisms for runtime configuration of spawners, have been split out and moved to the [`wrapspawner`](https://github.com/jupyterhub/wrapspawner) package
- Enable CI testing via Travis-CI

- Add `make_preexec_fn` method as an avenue for overriding pre-exec actions,
e.g. setting resource limits. Default behavior is unchanged.

- Fix bug preventing JupyterHub 0.8 from connecting to Spawners with default `ip`.

- Remove deprecated code for supporting JupyterHub < 0.7.
JupyterHub ≥ 0.7 is required.

- Avoid invoking sudo for poll