Implicit groupby

[josh-swerdlow]

Types of changes

• New feature (non-breaking change which adds functionality)
• My code follows the code style of this project.
• [ X ] My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

I stripped the functionality inherent of in the groupby builtin plugin to use within our plugin.

Now, whenever one branches on a given parameter, the manifest will automatically re-group the inputs so there
is no duplicate timestamps in any given group.