Fixed misleading view name dd_inference_variables_mapped_weights to
dd_inference_weights_mapping

- Fixed code and documents
- Kept the original view also, for backward compatibility
Fixed a broken link in Makefile installation
Fixed json_extractor to include null values in extractor input

We used to intentionally eliminate fields in a row where value
is null in JSON extractor input. Now we want to include these
fields with null values.

For example, for a table a(x, y), if a row is (1, NULL), the
json_extractor input for this row used to be {"x": 1}. Now our input is
{"x": 1, "y": null}.
Merge pull request #163 from HazyResearch/hotfix-jsonextractor-null

Fixed json_extractor to include null values in extractor input.

Also when no factors are active in the default pipeline, do not run the sampler.
Merge pull request #162 from HazyResearch/zifei-mariadb

Fixed misleading view name for weights view
Updated spouse_example/tsv_extractor to be coherent with
default_extractor

- Now the two implementations should generate same results.
Fix filename argument to unload() to unbreak the use of inference.parallel_grounding
Avoid warning from mv when not using inference.parallel_grounding
Fixed cleaning command for parallel grounding
Spouse example for psql/gp; draft of gp test architecture

- Added a test of psql spouse example
- Added test_gp.sh script
Fixing examples to let GP test work

- Mostly dealing with COPY / \\COPY issue. COPY has permission problems on GP.
- For Chunking, have not fixed the issue yet. Now on GP, chunking test will fail for both with/without parallel grounding.
Add support for --quiet for linux sampler

This is for travis test purposes.
Merge pull request #164 from HazyResearch/zifei-grounding-test

Added tests for Greenplum
Mindtagger examples for has_spouse precision tasks
Documented Mindtagger for Labeling Data Products
Merge pull request #165 from HazyResearch/netj-mindtagger-example

Added Mindtagger example and documentation
Merge branch 'develop' into release-004