Format git log as JSON

Table 2-1 on http://git-scm.com/book/en/Git-Basics-Viewing-the-Commit-History lists some of the options that --pretty=format takes.

```
%H Commit hash
%h Abbreviated commit hash
%T Tree hash
%t Abbreviated tree hash
%P Parent hashes
%p Abbreviated parent hashes
%an Author name
%ae Author e-mail
%ad Author date (format respects the --date= option)
%ar Author date, relative
%cn Committer name
%ce Committer email
%cd Committer date
%cr Committer date, relative
%s Subject
```

We can use this to extract git commit history in a JSON parseable format.

```
git log --pretty=format:'{"author date": "%ad","author e-mail": "%ae","author name": "%an","commit hash": "%H","committer date": "%cd","committer email": "%ce","committer name": "%cn","subject": "%s"}'
```

Which outputs eg.

```
{
"author date": "Tue May 7 13:42:17 2013 +0100",
"author e-mail": "me@mine.com",
"author name": "JamieMason",
"commit hash": "b151819d7e19b97b4d05c4c3aeec76a71054a8f2",
"committer date": "Tue May 7 13:42:17 2013 +0100",
"committer email": "me@mine.com",
"committer name": "JamieMason",
"subject": "various docs, notes, discussions"
}
```

Start with the project's history-replay entry point, which is not identified in the issue, and compare its behavior with the shown git log --pretty=format command. Determine where JSON output belongs; done means the replayed commit history can be emitted using the listed fields and parsed as JSON.

Written by the indexing model from the issue text.