Update relative path calculation to properly account for case-insensitive file systems
Update blob lookup to properly account for case-insensitive file systems
Merge pull request #58 from sharwell/case-insensitivity

Case insensitivity
Add a VSPackage to the project (required for menu commands and options pages)
Define toolbar commands for the Git Diff Margin actions
Use IVsToolbarTrayHost to provide the toolbar functionality
Add CommandFilter and TextViewCommandFilter helper classes
Implement diff margin commands using a text view command filter (fixes #8)
Enable the diff margin separately from the selection margin
Make sure the text editor is focused after a rollback
Make GitDiffMarginTextViewOptions a static class
Implement the internal commands "Toggle Compare to Index", "Compare to Index", and "Compare to Head"
Add the Toggle Compare to Index button to the diff tool bar, other placements TBD (fixes #35)