v0.45

 - Update libgit2 to 73dd663 (GH#126,GH#137)
 - Added Walker methods (GH#127):
    + sorting
 - Added Index::Entry methods (GH#130):
    + blob
 - Added Graph methods (GH#131,GH#132):
    + ahead()
    + behind()
    + ahead_behind()
 - Added Commit methods (GH#134,GH#138):
    + as_email()
    + diff()
 - Added Blob methods:
    + is_binary()
 - Added Walker methods (GH#140):
    + all()
 - Added methods:
    + message_prettify()
 - Removed Remote methods (GH#135) (Incompatible change):
    + is_url_valid()
 - Index -> write_tree() now returns a Tree object (GH#128). A stringify
   overload has been provided for compatibility
 - Repository -> merge_base() now returns a Commit object (GH#129)
 - Commit, Tree and Blob now have overloads for equality and stringify (GH#129)
 - Index -> conflicts() now returns Index::Conflict objects (GH#130)
   (Incompatible change). The documenation was actually incorrect, a list
   of hashes was returned whereas the documenation stated a list of
   Index::Entry objects.
 - Try to support WinHTTP on Windows
 - Remote's update tips callback now set $a or $b to undef if the
   reference was created or removed (Incompatible change) (GH#136)
 - Added extra diff flags (GH#138)
 - Remote -> load() used to consider a missing remote as an error.
   It now returns undef instead of die'ing. (Incompatible change) (GH#139)
 - Tag -> foreach() now also returns lightweight tags (GH#141,GH#142)
 - Reference -> is_tag() was broken for lightweight tags (GH#142)