conf: Add a spec file for creating rpm packages from Disco.

This sepc file can be used to create a couple of rpm packages to be used in the
rpm-based distributions.
This rpm file is experimental and has only been tested on a Centos system.
doc: Add some info to the basic installation guide.
Merge pull request #474 from pooya/rpm

conf: Add a spec file for creating rpm packages from Disco.
doc: Add tentative release notes for 0.5.1.
Merge pull request #475 from pooya/0.5.1

0.5.1
Adding changelog and requires
Merge pull request #478 from pooya/spec

Adding changelog and requires
modutils: Try to find and import the module originating a file.

This should resolve issue #467.
modutils: Move the get_modules function to the parent worker.

This way, both the classic and pipeline worker should work fine.
Merge pull request #481 from pooya/467

467
Makefile: Export the variables necessary for deb pkg.

This should resolve issue 479.
worker: Fix the logic of saving the output of stages.

Do not save the output of the job in the python library.  If the save_results
is set, the outputs of the job are already saved.
worker: Set the save_info in the parent Worker class.

This lets both the pipeline and the classic worker use it.
hdfs: Use a unique name for different parts of the output of a job.
worker: Add a missing import to task_io.
jobpack: Add the save_results to the jobpack in the Parent worker.
Examples: Add a version of wiki reader that saves the output.
Merge pull request #483 from pooya/save_results

Save results
job coordinator: Use task_outputs for simplicity.

This change should not have any functional effects.
python lib: Add a scheme for redis.

Now disco can read the inputs from a redis key value store and write the outputs
to it.  The application is limited because the key-value store is not the most high
throughput storage option.