add name_only arg

[janthmueller]

Need to enhance swizzledtuple by adding a name_only argument (or a similarly named option) to indicate that only the names get swizzled, skipping the current sequential matching algorithm that tries out all possible names. This should make the swizzle_attributes_retriever method much faster.

Alternatively, introduce a swizzle_only argument that accepts multiple values like dir. This would allow swizzledtuple to grab all the attributes via dir, bypassing the sequential matching and further speeding up the swizzle_attributes_retriever method. This change would make it more convenient for swizzled classes, not just for named tuples.

Maybe add an option to specify dir or provide a list of attributes to swizzle to make the process faster.
(Also need to research the Python C API to find ways to make the entire swizzling process faster.)