This pull does two major things:
1. Refactors `serialize_params` to be more concise and readable while
still complying to our existing test suite. Unfortunately over time
this method has become a ball of mud that's very difficult to reason
about, as recently evidenced by #384.
2. Moves `serialize_params` from class method to instance method (while
still keeping for old class method for backwards compatibility). This
is to give it a more sane interface.
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