Open a stream to write an object into the ODB
The type and final length of the object must be specified when opening the stream.
The returned stream will be of type GIT_STREAM_WRONLY
, and it
won't be effective until git_odb_stream_finalize_write
is called
and returns without an error
The stream must always be freed when done with git_odb_stream_free
or
will leak memory.
0 if the stream was created; error code otherwise