Appending change_files parameter which describes changed files in the updated commits

[userlocalhost]

This is the change for #11.

The main points of this change are following.

• Appending new parameter changed_files which describes manipulated files within the updated commits for each operation type 'add', 'delete', 'moved', 'modified' to the dispaching payload.
  But currently this feature is workable only with the BitBucket Server. I should be able to implement equivalent feature for the BitBucket cloud.

• Correcting the payload format which is written in the README. Previously, the only commits parameter value which is a parameter of dispatching payload was described in the README. Then, I corrected it to describe whole payload format and added new parameters changed_files and files.
  The files is the parameter which describes manipulated files in the target commit. And changed_files means the all manipulated files within the whole updated commits by omitting the overlapping.

Thank you.

[Kami]

Nice work - thanks.

Will have a look shortly.

[Kami]

It looks like the trigger format hasn't changed and it's not backward compatible, right?

[Kami]

Actually, looking at the code changes below it looks like it didn't really change, just a new key was added and readme was out of date.

[Kami]

Build appears to be failing (lint issue), besides that, LGTM 👍

[userlocalhost]

Thank you for your review and pointing it out!

Below the payload parameter of trigger format was omitted in the repository_sensor.yaml. And the payload parameter which is described in the README was different with the implementation, as you mentioned.

I specified the trigger format in detail and corrected the README description for up to date.

Thank you.