Support git repositories which use the sparse checkout git feature

[EugeniyMaksimov]

Hello!
Git introduced a new feature called sparse-checkout This command is very useful in large repositories containing a lot of projects. Using sparse-checkout and partial repository clone allow substantially reduce occupied by the repository space on local disk.

GitDiffMargin is a useful extension for Visual Studio, This extension uses the libgit2sharp. The extension is not work with repositories uses sparse-checkout because such repositories are not supported.

Reproduction steps

Git Diff Margin get an exception unsupported repository version 1. Only versions up to 0 are supported. while creating a Repository on this line.

Refer to the according GitDiffMargin issue for more info:laurentkempe/GitDiffMargin#356

[mattjohnsonpint]

Looks like format version 1 was added in libgit2/libgit2#5388, included with libgit2 v1.1.0. So when libgit2sharp gets updated next, it should be included.