Track committer and author

[flyingzumwalt]

dat should, track committer and author like git. Even if it doesn't set them by default, allow users to pass in the values with --committer, and --author flags and store the values in leveldb as "committer" and "author"

An import like this

dat import proteins.csv -d proteins --committer "C O Mmitter <committer@example.com>" --author "A U Thor <author@example.com>"

Would result in rows that look like this

{
    "content":"row",
    "key":"cifvfaopm000wflaecmb9k1gl",
    "version":"04c3301367d351bae0e8bb12bb8b15e9d0a025932d678282edb6b076097475fb",
    "committer":"C O Mmitter <committer@example.com>",
    "author":"A U Thor <author@example.com>",
    "value":{...data...}
}

and entries in the dat log like this:

Version: 04c3301367d351bae0e8bb12bb8b15e9d0a025932d678282edb6b076097475fb [+1, -0]
Author: "A U Thor <author@example.com>"
Date: Thu Oct 22 2015 12:23:13 GMT-0700 (PDT)

Why both author and committer?

The [git book]() explains

The author is the person who originally wrote the work, whereas the committer is the person who last applied the work. So, if you send in a patch to a project and one of the core members applies the patch, both of you get credit – you as the author, and the core member as the committer.

related to #121

[flyingzumwalt]

oops. wrong github project. see maxogden/dat#413