Add functions for removing parameters when trying new configurations.

[alvestrand]

This change makes the optimizer aggressively remove parameters, and gives slightly higher scores (0.000001 dB per parameter) for shorter parameter lists, leading the optimizer to prefer them.

It adds a function for marking parameters as mandatory, since some codecs function very badly with all parameters removed.

Addresses #4 .

[phoglund]

lgtm with nits fixed