Streaming log API now also honors history argument.

This addresses issue #56.

You know, I hate go's standard.  People have a limited short-term working memory, and descriptive names reduce the amount of data you have to keep in your head, which leaves working space for other concepts.  Carrying around 'c means commit' is one less slot your working memory has for 'that method actually modifies it's arguments' or some other relevant fact.