v0.21

 - Reference -> target(), Tree -> diff() and TreeEntry -> object() methods do
   not accept a Repository argument anymore (incompatible change)
 - Fix memory leak in Tree -> entry_bypath() (GH#11)
 - Tag -> delete() is now an object method just like other delete() methods
   (incompatible change)
 - Do not use Makefile.embed to build libgit2 to avoid FTBFS on *BSD
 - Update libgit2 to fd69c7b