benchmark: additions for buffers

Micro benchmarks have been added for all Buffer methods.
src: update and order benchmarks

Because of the previous disarray of benchmarks, this commit is not meant
to be a completed task. Instead it serves a couple purposes:

* Begin organizing existing benchmarks into folders by api category
* Convert obvious benchmarks to use the new standard api

A few new micro benchmarks have also been added to help test easily
iterative pieces of functionality.