Submodule libgit2sharp updated

Submodule libgit2sharp:
    > 8b13ff3 - Introduce repo.ObjectDatabase.CreateTag()
    > 96df5f8 - Update libgit2 binaries to 5aee963
    > 96553df - Add CompareOptions
    > e210b9b - Teach Repository.Reset to append to the Reflog
    > 7eba13d - Move AssertReflogEntryIsCreated to BaseFixture
    > 5331dea - Fix test with repository clone
    > 1787c61 - Enhance Index.RetrieveStatus() test coverage
    > e39a21d - Add type details to FilePathMarshaler error
    > c000936 - Mark TreeEntryTargetType.Tag as obsolete
    > 3f0efa0 - Fix HasAny() enum helper to ease migration to .Net 4.0
    > dc208c9 - Add test for TreeChanges case-sensitivity
    > 0394ec6 - Remove useless marshaling directive
    > 88cf0d9 - Remove obsolete methods
    > 02638bb - Upgrade NuGet.exe to version 2.5.40416.9020
    > 73b4889 - Release LibGit2Sharp v0.11
    > 5c26149 - Fix documentation
    > efb3ecc - Update libgit2 binaries to b641c00
    > 92048f9 - Obsolete Tree.Trees and Tree.Blobs properties
    > fa1f266 - Obsolete GitObjectType
    > d6c74d2 - Deploy ObjectType to OdbBackend
    > 82a8d05 - Introduce ObjectType
    > b4aae4b - Obsolete TreeEntry.Type and TreeEntryDefinition.Type
    > 4e2a729 - Introduce TreeEntry.TargetType and TreeEntryDefinition.TargetType
    > 7df508d - Teach Refs.Add() to append to the reflog
    > ba6e5c9 - Remove SetIgnoreCaseOrSkip test helper
    > fb13e4e - Introduce IsFileSystemCaseSensitive test helper
    > 023eaf4 - Prevent repo.Lookup() to accept GitLink as a target type
    > 1465bf3 - Add extension methods to determine reference kind
    > af00576 - Add helper methods to determine reference kind from canonical name
    > 9593179 - Refactor handling of reference prefixes
    > 718a99e - Move Repository.Conflicts to Index.Conflicts
    > 95430a1 - Teach UpdateTarget() to append to the reflog
    > 5960c38 - Code style cleanup
    > bccacb9 - Teach Checkout() to append to the reflog
    > 0efaf0d - Fix Checkout behavior when dealing with Head
    > cd0a909 - Enforce checkout test coverage
    > d3c6da5 - Enforce reference lookup test coverage
    > 4d92ed4 - Move BuildSignatureFromGlobalConfiguration() to Configuration
    > 902ed7d - Teach Checkout() to cope with revparse syntax
    > d5c4a44 - Add TreeDefinition.Add(Submodule)
    > 0058041 - Add TreeDefinition.AddGitLink()
    > 6d5efba - Proactively call git_submodule_reload()
    > 9a7b31d - OCD: Head > Index > WorkDir
    > da2a8d3 - Add BaseFixture.SubmoduleTestRepoWorkingDirPath
    > 56eb34b - Add test to ensure conflicts are cleared when calling Index.Remove()
    > bd1ef45 - Add BaseFixture.CloneMergedTestRepo()
    > ff7bc1d - Cleanup ConflictFixture
    > 6b53e32 - Switch internal implementation of Index.Remove() to git_index_remove_bypath()
    > 88c5862 - Move Index.Remove() tests to a separate file
    > 68fe9f4 - Improve support for git rm --cached semantics
    > bdf2418 - Make Index.Remove() able to remove only from index
    > af02e4e - Make Index.Remove() able to remove folders
    > 1e1607b - Allow passing ExplicitPathsOptions to Index.Remove()
    > 068d495 - Make Index.Remove() diff-based
    > 6a02dd8 - Add RemoveFromIndexException
    > 1e2bdea - Insert new reflog entry on merge commit
    > 2dd033f - Reflog entries can't be >1 line
    > b448cf0 - Fix .mailmap
    > f1cbebf - Linux build: clean directory before build as it may exist already.
    > ddc6238 - Fix incorrect obsolete message
    > 74f3bb1 - Align Proxy methods name to libgit2 ones