v0.33

 - Fix segfaults caused by invalid object creation (GH#66) (thanks, @pipcet!)
 - Add Config -> default() method (GH#67) (thanks, @magnolia-k!)
 - Do not fail when a lightweight tag is found in the Tag->foreach() callback
   (GH#68) (thanks, @pipcet!)
 - Add Tree::Entry -> file_mode() method (GH#69) (thanks, @pipcet!)
 - Repository -> merge() now takes %merge_opts and %checkout_opts as 2
   separate parameters. (incompatible change) (GH#70)
 - Merge options parameter member 'automerge' has been renamed to 'favor',
   inline with libgit2 API changes. (incompatible changes) (GH#70)
   It has also learned about a 'union' merge.
 - Checkout options has learned new options: 'target_directory', 'ancestor_label',
   'our_label' and 'their_label'. (GH#70)
 - Checkout strategy has additional options: (GH#70)
   'use_ours', 'use_theirs', 'skip_locked_directories', 'dont_overwrite_ignored',
   'conflict_style_merge', 'conflict_style_diff3' and 'disable_pathspec_match'.
 - Added new Repository methods (#GH70):
    + Repository -> merge_analysis()
    + Repository -> merge_base()
 - Added new Index methods (#GH70):
    + Index -> write_tree_to()
    + Index -> checkout()
    + Index -> entries()
    + Index -> add_conflict()
    + Index -> remove_conflict()
 - Added new Commit method (#GH70):
    + Commit -> merge()
 - Added new Tree method (#GH70):
    + Tree -> merge()
 - Index -> add() now either takes a path or a Index::Entry (GH#70)
 - Remote->create_inmemory() has been replaced by Remote->create_anonymous()
   (incompatible change) (GH#71).
   The order of 'url' and 'fetchspec' has also been reversed to bring it
   inline with the upstream changes.
 - Update libgit2 to bcc6229