Allow query parameters to be passed to custom changes filters

[smithsz]

Checklist

• Tick to sign-off your agreement to the Developer Certificate of Origin (DCO) 1.1
• Added tests for code changes or test/build only changes
• Updated the change log file (CHANGES.md|CHANGELOG.md) or test/build only changes
• Completed the PR template below:

Description

Allow arbitrary query parameters to be passed to custom changes filters.

Fixes #402.

Approach

Add new ANY_ARG and ANY_TYPE to list of valid changes arguments:

_CHANGES_ARG_TYPES = {
    'conflicts': (bool,),
    'doc_ids': (list,),
    'filter': (STRTYPE,),
    'include_docs': (bool,),
    'style': (STRTYPE,),
    ANY_ARG: ANY_TYPE  # pass arbitrary query parameters to a custom filter
}

Schema & API Changes

No change.

Security and Privacy

No change.

Testing

Includes additional unit test.

Monitoring and Logging

No change.

[smithsz]

This test is no longer valid as passing foo='bar' is now accepted under ANY_ARG: ANY_TYPE.

[ricellis]

+1, but please add the missing copyright update

[ricellis]

This needs a copyright update

[emlaver]

@smithsz There's a couple cases that cause a CloudantArgumentError ___ type is not callable:

feed = Feed(self.db, foo={}) # type is dict
feed = Feed(self.db, foo=object_var) # type is object

We should probably only allow int, float, string, and bool types.

[smithsz]

I think we should serialise foo={}. Obviously serialising foo=object() will never work and should throw.

How about making json.dumps the default type converter?

[emlaver]

Looks good