Submodule libgit2sharp updated

Submodule libgit2sharp:
    > 9f0daeb - Release LibGit2Sharp v0.13.0
    > 7e5bbbf - Teach Repository to Checkout paths
    > 01dfa28 - Ensure there is a self cleaning directory to remove
    > 399384d - Teach Checkout() to cope with revparse extended syntax leading to references
    > 6574cfb - Update libgit2 binaries to 7940036
    > 90d7f06 - Remove ".dll" extension from dll-name declaration
    > 9fa5391 - Ensure libgit2 always uses STDCALL convention
    > afb9cf4 - Update UniqueIdentifer.targets to be called from arbitrary directory
    > 384ce73 - Teach UpdateLibgit2ToSha.ps1 to take arbitrary libgit2 library name.
    > a496c1c - Update libgit2 binaries to bd67979
    > 1d4d35a - Make Stash expose Base, Index and Untracked commits
    > b0086f3 - Refactor Travis build script
    > df84243 - Make RelWithDebInfo the default libgit2 build flavor
    > fd398ef - Favor Constants.Signature over BaseFixture.DummySignature
    > be0b83c - Make build.libgit2sharp.sh executable
    > dcafac6 - Cleanup usings
    > 6fbd65b - Standardize comments style
    > 219b0c5 - Rename CheckoutOptions into CheckoutModifiers
    > d05b0da - Rename DiffOptions into DiffModifiers
    > fa5eb6a - Rename StashOptions into StashModifiers
    > 6a257ed - Rename GitSortOptions into CommitSortStrategies
    > 7d9baab - Rename Filter into CommitFilter
    > 8dfa16f - Reintroduce obsolete method to avoid breaking change
    > 5b32d27 - Simplify Proxy.git_commit_create() implementation
    > 1b418ae - Obsolete repo.Clone() overload which returns a Repository
    > 09a26cf - Obsolete repo.Init() overload which returns a Repository
    > 3c7c424 - Teach Repository.Init() to set up a separate git directory
    > ca7470b - Teach checkout to report notifications
    > d321e93 - Add strongly typed UserCanceled exception
    > 7a90218 - Create a new repo.Checkout() overload which accepts a Commit object
    > 5e40bff - Add InitNewRepository() test helper
    > f62b134 - Leverage Touch() to generate test files
    > d7e70a4 - Make Touch() overwrite potential existing file
    > 9a81dab - Make BaseFixture.Touch() return the full filepath
    > 2bc52bb - Allow ObjectDatabase.CreateBlob() to limit the number of bytes to consume
    > a6714db - Obsolete ObjectDatabase.CreateBlob(BinaryReader, string)
    > b60f9f6 - Make ObjectDatabase.CreateBlob() accept a Stream
    > e2aeb98 - Rename ObjectDatabase.CreateTag into ObjectDatabase.CreateTagAnnotation
    > 7b8472d - Touch() should ensure parent directory exists
    > 39716ec - Introduce repo.Refs.RewriteHistory()
    > ede53d8 - Ensure built binaries names match with resources
    > a3a989a - Use CopyNativeDependencies.targets for LibGit2Sharp.Tests
    > 3f49b5f - Add CopyNativeDependencies.targets
    > 2a4abe0 - Introduce repo.Refs.ReachableFrom()
    > 0b253d7 - Introduce TreeDefinition.From(Commit)
    > 284e37a - Fetch should respect the remote's configured tagopt setting unless explicitly specified
    > f70cede - Expose TagFetchMode property on Remote type and include mechanism to update it.
Creating new remote fixed. Closes #1679