add ability to use as a cli app

[ctomkow]

• Include the feature to pipe data into the cli app, like typical *nix tools allow. This would allow for chaining of commands.
  curl my.api.with.highly.nested.json.response | jsonparse --find_key_chain ['my', 'key', 'chain']

• Also, support the ability to provide a file of JSON as a flag.
  jsonparse --file my.json --find_key 'mykey'

[ctomkow]

• Working cli interface, currently released as 0.12.0.dev1.
• todo:
  • documentation of functionality.
  • output each found item on a separate line (as opposed to a list like the library does)

[ctomkow]

todo: modify cli help message on key-value error, complaining about not valid json. I prefer '"test"' over \"test\"

[ctomkow]

cli interface added in release 0.12.0