I added multiple failing tests cases to tests/libgit2/blame/buffer.c to cover the test cases.

blame.c has been updated to get these tests to pass. 
Fixes include:
    shift_hunks_by now no longer shifts hunks before the start line. 
    Adjusting the wedge line in the case where a new hunk deletes and adds lines.
    In buffer_line_cb for addions humks are now shifted after the current diff line.
    Fixing the logic for removing a line in buffer_line_cb to work with multi-line deletions.