Making the standalone api nicer to use

[shana]

I did a little app (https://github.com/shana/unity-runtime-git) to test using the api at runtime, and I had to do some tweaks to make it nicer to use. These are those tweaks:

• When parsing the history log, the first line of the commit was being added to the description. This makes it annoying to show entries when showing both the first line (summary) and the body (description), as the first line would appear duplicated. I kinda wanna treat these as email subject and body (because that's what they were meant to be originally in git anyways), so took out the duplication.
• calling InitializeRepository(path to repository) on DefaultEnvironment does the useful thing of setting the base path on the FileSystem object, which means any shell commands and path manipulations are going to assume that path to repository as the base for all relative paths and working directory paths. Which is handy! Only the logic that we currently have makes it impossible to call InitializeRepository twice (it just ignores it), so it's not easy to switch these paths.
• The task classes should be public, they're useful!

[StanleyGoldman]

Looks good, otherwise one nit pick.

Fixed?