An Object should be about representing a libgit2 object rather than
showing which methods it should support.
Change any return of Object to *Object and provide methods to convert
between this and the particular type.
While Go will assign the correct type to a const block when it
auto-creates the values, assigning makes the const be typeless and will
only gain it in each particular use.
Make each constant in the blocks have an assigned type.
Carlos Martín Nieto
David Calavera