Merlin

Added
- cli test flag `--local`, which can be used in place of listing out the id of each
local cli test.
- A Merlin Dockerfile and some accompanying web documentation.
- Makefile target `release`.
- The merlin config now takes an optional --broker argument, the
value can be None, default rabbitmq broker, or redis for a redis
local broker.
- Missing doc options for run and run-workers.
- Check server access when `merlin info` is run.
- A port option to rabbitmq config options.
- Author and author_email to setup.py.

Removed
- Makefile targets `pull` and `update`.
- Unneeded variables from `simple_chain.yaml`.
- All `INFO`-level logger references to Celery.

Changed
- Updated the Merlin Sphinx web docs, including info about command line commands.
- Example workflows use python3 instead of python.
- Updated `merlin info` to lookup python3 and and pip3.
- Altered user in Dockerfile and removed build tools.
- MANIFEST.in now uses recursive-include.
- Updated docker docs.
- `make clean` is more comprehensive, now cleans docs, build files, and release files.
- The celery keyword is no longer required in `app.yaml`.

Changed
- Adjusted `maestrowf` requirement to `maestrowf>=1.1.7dev0`.

Removed
- Unused directory `workflows/` at the top level (not to be confused with
`merlin/examples/workflows/`)

Fixed
- Bug related to missing package `merlin/examples/workflows` in PYPI distribution.

Fixed
- Bug related to a missing path in `MANIFEST.in`.
- Error message when trying to run merlin without the app config file.

Added
- `version_tests.sh`, for CI checking that the merlin version is incremented
before changes are merged into master.
- Allow for the maestro `$(LAUNCHER)` syntax in tasks, this requires the
nodes and procs variables in the task just as in maestro. The LAUNCHER keyword
is implemented for flux, lsf, slurm and local types. The lsf type
will use the LLNL srun wrapper for jsrun when the lsf-srun batch type
is used. The flux version will be checked to determine the proper format
of the parallel launch call.
- Local CLI tests for the above `$(LAUNCHER)` feature.
- `machines` keyword, in the `merlin.resources.workers.<name>` section. This allows
the user to assign workers (and thence, steps) to a given machine.
All of the machines must have access to the `OUTPUT_PATH`, The
steps list is mandatory for all workers. Once the machines are added, then only
the workers for the given set of steps on the specific machine will start. The
workers must be individually started on all of the listed machines separately by
the user (`merlin run-workers`).
- New step field `restart`. This command runs when merlin receives a
`$(MERLIN_RESTART)` exception. If no `restart` field is found, the `cmd`
command re-runs instead.

Fixed
- A bug in the `flux_test` example workflow.

Changed
- Improved the `fix-style` dev Makefile target.
- Improved the `version` dev Makefile target.
- Updated travis logic.
- `MERLIN_RESTART` (which re-ran the `cmd` of a step) has been renamed to `MERLIN_RETRY`.

Added
- Makefile target `version` for devs to auto-increment the version.