This should make it clearer what the return value implies.

The push cannot be successful if we sent a bad packfile. We should
return an error in that case instead of storing it elsewhere.

Introduce stackable IO streams

We currently have gitno for talking over TCP, but this needs to know
about both plaintext and OpenSSL connections and the code has gotten
somewhat messy with ifdefs determining which version of the function
should be called.

In order to clean this up and abstract away the details of sending over
the different types of streams, we can instead use an interface and
stack stream implementations.

We may not be able to use the stackability with all streams, but we
are definitely be able to use the abstraction which is currently spread
between different bits of gitno.

doc: add documentation to all the public structs and enums

The iterator is the last argument. There is also no returned notes, just
ids, so the comment about freeing is out of place.

Make it consistent between git_note_create() and git_note_remote() by
putting it after the repository.

This makes them show up in the reference, even if the text itself isn't
the most descriptive.

These have been found with

    grep -Przon '\n\ntypedef struct.*?\{' -- include
    grep -Przon '\n\ntypedef enum.*?\{' -- include

Spelling fixes