Fixes #30.

1. The protoc include dir of the protobuf repo is the src subdir
   of the repo, not its root.

2. bash allows only one trap command per signal, so arrange to
   delete both temporary repo dirs with one command.

* reimplement regen

* regenerate files

This change should fix our ongoing problem with duplicate file names causing failures.

At the moment, this changes requires you to build protobuf from source with this patch to work. Otherwise, we won't be able to properly import descriptor.proto.

- all proto files are deleted, as the new logic does not need to rewrite any part of the proto files.
- google.protobuf.descriptor is removed; it's official home is github.com/golang/protobuf/protoc-gen-go/descriptor.
- the protobuf directory is split into multiple packages. This is a breaking change.

sed's -i flag differs on platform. Switch based on platform.

(Also moved api/distribution which had ended up in the wrong spot).

Fixes #5

Add back the appengine API.

Split up the rpc directory into its individual components.
Disable three APIs known to be currently broken in the upstream repo.

The proto files within are dervied from:
  https://github.com/google/protobuf
  https://github.com/googleapis/googlapis