benchmark: include bench-timer as external

bench-timer has been made external and included as a module.

The api has been heavily extended and all tests that use is have been
updated.
benchmark: add and organize buffer methods

Benchmarks have been created for all Buffer methods. They have also been
placed into benchmark/buffer. The single Typed Array test has been moved
to benchmark/typedarray.
benchmark: add and organize net tests

Benchmarks for the net module have been added or moved to the
benchmark/net directory.