Proto commits in allenai/spv2

These 5 commits are when the Protocol Buffers files have changed:

Commit:efe30cb
Author:Dirk Groeneveld

Clearer distinction between doc_name and doc_sha

The documentation is generated from this commit.

Commit:395e5cd
Author:Dirk Groeneveld

Handle errors more gracefully

Commit:7c93a15
Author:Dirk Groeneveld

Handle errors in processing

Commit:3326760
Author:Dirk Groeneveld

Make a server out of the PDF preprocessing

Commit:4425ad5
Author:Dirk Groeneveld

Adds dataprep project