Ability to avoid deriving/implementing a trait for specific types

[fitzgen]

This is a meta tracking issue for all the different traits that we allow deriving. Right now its always everythign or nothing. We have issues open for allowing specifying certain types that we want to omit implementations for.

• Debug: Allow specifying certain types we shouldn't derive/impl Debug for #961
• Copy: Allow specifying certain types we shouldn't derive/impl Copy for #962
• Default: Allow specifying certain types we shouldn't derive/impl Default for #963
• Hash: Allow specifying certain types we shouldn't derive/impl Hash for #964
• PartialEq: Allow specifying certain types we shouldn't derive/impl PartialEq for #965