Support package.json autodiscovery (default)

Closes #53

commit e80dbfd9caa56edc3c9980622e6ebffecbc6e104
Author: Rhys Arkins <rhys@keylocation.sg>
Date:   Tue Jan 17 09:11:03 2017 +0100

    Update docs

commit 78830806efe35150e9ec4cb5416d43092ccf0fc7
Author: Rhys Arkins <rhys@keylocation.sg>
Date:   Tue Jan 17 08:52:23 2017 +0100

    Refactor

commit c44979212f7c51d395a4b4dbffe831af5467b4fc
Author: Rhys Arkins <rhys@keylocation.sg>
Date:   Tue Jan 17 07:25:28 2017 +0100

    Set default packageFiles to []

commit c830f0b37928460ed857260e6c4b4c3c23443f1e
Author: Rhys Arkins <rhys@keylocation.sg>
Date:   Tue Jan 17 07:14:33 2017 +0100

    Add github.fileFile