Luigi

This version contains mostly bugfixes, in particular making Luigi 2.0 working on Windows

Thanks daveFNbuck econchick Tarrasch dlstadther DeaconDesperado jpiper nresare dhurlburtusa stephenpascoe mbruggmann and some more people I probably forgot!

Pull requests
- 1441 don't print nested stack traces
- 1439 spark: use list2command
- 1447 fix unix socket
- 1446 fix daemon
- 1448 support symlinks in hdfs
- 1431 1433 worker as a context manager
- 1429 keyboardinterrupt fix
- 1428 make it work without tornado
- 1425 positional parameter qualification
- 1422 fixed broken task trigger
- 1411 mention misspelled task name
- 1418 bigquery fix
- 1417 visualizer fix
- 1413 kwargs for s3
- 1345 retry get_work
- 1315 limit graph size
- 1391 amazon sns support
- 1392 pyspark parameter fix
- 1395 tornado fix
- 1397 spark package fix
- 1400 serialize TaskParameter
- 1402 kwargs for boto s3
- 1388 disable email from cfg
- 1341 get_work fix
- 1340 stop subprocesses on exception
- 1352 fix bug in scheduler
- 1357 fix issues in requires during scheduling
- 1367 fix visualizer w weird task names
- 1372 s3target.path
- 1314 redshift updates
- 1370 gmail authentication for notifications
- 1366 pig fix
- 1331 path warning fix
- 1338 ssh forwarding agent
- 1337 ssh multiplexing
- 1363 windows signal fix
- 1298 tracking fix
- 1346 fix dep graph on firefox

Highlights:
- Improved documentation.
- New visualiser page! https://github.com/spotify/luigi/pull/1086, thanks stephenpascoe
- Execution summaries at end of runs! https://github.com/spotify/luigi/pull/1091, thanks nicolehedblom
- Smarter layout algorithm for the SVG dependency graphs, thanks daveFNbuck
- Command line interface now has a useful --help, see https://github.com/spotify/luigi/pull/1276
- Luigi finally has semantic exit codes! https://github.com/spotify/luigi/pull/1264

Contrib:
- Stablization of GCP tools
- AWS EC2 support. https://github.com/spotify/luigi/pull/1317, thanks jfeala
- Sungrid support. https://github.com/spotify/luigi/pull/1124, thanks jfeala (again :))

Scheduling:
- UNIX sockets are now supported, hence also encryption. https://github.com/spotify/luigi/pull/1129, thanks graingert
- Smarter scheduling! https://github.com/spotify/luigi/pull/1272
- Speedup in scheduler. https://github.com/spotify/luigi/pull/1046
- A `--take-lock` option to smoother roll out code changes. https://github.com/spotify/luigi/pull/1137

Deprecations:
- There have been a lot of deprecations of features regarding Parameters. Before upgrading, please consider taking a look at the new [module documentation for parameters](http://luigi.readthedocs.org/en/stable/api/luigi.parameter.html).

Notable changes:
- `is_global` finally removed! (It still exists to not break old code, but it only sets `positional=False`)
- Initial support for Google Cloud Storage and Google BigQuery. Thanks mikekap! https://github.com/spotify/luigi/pull/999 https://github.com/spotify/luigi/pull/1002
- Massive luigid speedup for `get_work()` response times. https://github.com/spotify/luigi/pull/986
- Various bugfixes.
- Standardized FileSystem/Target interface. Again thanks mikekap! https://github.com/spotify/luigi/pull/997
- SQLAlchemy works for multiple engines. Thanks dylanjbarth! https://github.com/spotify/luigi/pull/991

Same as v1.2.1. Only that we can't have a initial "v" as otherwise readthedocs won't build the documentation for us. See https://github.com/spotify/luigi/issues/970#issuecomment-105623162

Notable changes:
- Dropped Python 2.6 support. https://github.com/spotify/luigi/pull/934
- New experimental ["assistant"](https://github.com/spotify/luigi/blob/ac530c6cb3ac4df81ad236817373bdac19effa6d/luigi/interface.py#L104) feature.
- External tasks are now also registered. This might cause breakage in settings like described [here](https://github.com/spotify/luigi/pull/880#issuecomment-94008171)
- Many configuration settings have been hoisted to the new configuration system. Particularly for hdfs-related parameters. The `--help` command will show what new options are available.
- While `is_global` is not removed yet. It'll get removed anytime soon. Please use the new `positional=False` setting as a replacement in your parameters. In fact, we suggest to always use `positional=False`.
- The central scheduler now supports searching within groups. https://github.com/spotify/luigi/pull/903
- New dependency graph rendering using D3. https://github.com/spotify/luigi/pull/920
- The built in map reduce framework can now use `ujson` instead of doing `eval`. It's still not clear to us how much faster it is. https://github.com/spotify/luigi/pull/939
- Various bug fixes and other features.