Add JSON as supported format for storing inventories, etc

[pombredanne]

This is often easier to handle than a set of ABOUT YAML files when they are not stored in the codebase and is a single file.

[chinyeungli]

@pombredanne can you provide a sample of what will the JSON input looks like?

[chinyeungli]

The JSON support represent both input and output

[mjherzog]

The use case is to store the ABOUT content in a file, rather than a set of files, to simplify use of an ABOUT.JSON file as a mini-database for recording the results of some analysis for a product release.
The record layout within the JSON file should be quite similar to its current ABOUT file layout. We need to include optional fields, but not sure how to handle custom fields.

[chinyeungli]

The use case is to store the ABOUT content in a file, rather than a set of files...

This is basically the same as the inventory command which store the ABOUT content in a CSV file.
Added support to output JSON format from inventory command.

[chinyeungli]

The next step is to add support to read JSON file to generate ABOUT files.

[chinyeungli]

JSON support for inventory, gen, and attrib are integrated.