Release 0.19.1

API changes:

- Rename Commit._message to Commit.raw_message
- Rename Signature._name to Signature.raw_name
- Rename Signature._email to Signature.raw_email

New features:

- Remote.push(refspec)
- Tag.get_object()

And some bugs fixed.

Thanks to Brodie Rao, Fraser Tweedale, Andrew Chin and Carlos Martín
Nieto.
Add additions and deletions for patch.
Add binary for patch.
Add binary for blob.
the number of deltas/patches in one diff
Merge remote-tracking branch 'xtao/binary'

Conflicts:
	src/types.h
Rename Patch.binary to Patch.is_binary for consistency
add len(diff) instead of diff.size
Merge remote-tracking branch 'alexband/size'
Merge remote-tracking branch 'xtao/blob'
Rename Blob.binary to Blob.is_binary for consistency
status: don't use the callback version

This allows us more straightforward code as well as returning NULL on
error with much less hassle than it would take with the callback
version.
Merge remote-tracking branch 'carlos/status-list'
reference: add a shorthand property

Add Reference.shorthand to make it simpler to present a human-readable
name for a particular reference.
Add append_log to reference.
Add Blame support
Merge remote-tracking branch 'xtao/reflog'
Make Reference.log_append signature more consistent

Consistent with the rest of the pygit2 API.
Adjust to libgit2 development branch

This wraps the previous functionality, though there are some iterator
changes we might still want to bring over.
Branch: move from foreach to the iterator