Make Timer class private
Add {_get,_set,_has,_init}_by_field methods for faster field access
Various speedups to StructReader/Builder
Fix up various bugs that arose when trying to `cimport capnp`
Change addressbook benchmark around a bit
Initial version of code generating plugin

The plugin generates higher performance compiled versions of the structs
Speed up code generated modules even more.

Switch to using generated c++ capnp code
Rename setup.py template to setup.py.tmpl to avoid confusion
Get code generator plugin to a decently working state.

Still a few outstanding performance issues, and imports inside .capnp
files may not be working