Issue #66: Rewarder composition

[Mark2000]

Description

Closes #66

Allows for multiple rewarders to specified.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How should this pull request be reviewed?

• By commit
• All changes at once

How Has This Been Tested?

Tests added to cover multiple rewarders.

Future Work

May encounter some compatibility issues with complex rewarder setup, these have been noted with TODO comments.

Checklist

• I have performed a self-review of my code
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation and release notes
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• If I changed an example ipynb, I have locally rebuilt the documentation

[Mark2000]

TODO: add release note

[LorenzzoQM]

Nice feature!