support reftable ref database

[hanwen]

reftable is a scalable format for the ref database. It would be nice to support it in go-git

See https://github.com/eclipse/jgit/blob/master/Documentation/technical/reftable.md

(I'm interested in working on this.)

[mcuadros]

@hanwen feel free to work on it. Thanks!

[hanwen]

status update: https://github.com/google/reftable has an implementation for the format.

[hanwen]

I've started talks with libgit2 and git-core folks, see https://public-inbox.org/git/xmqq4kx4z8n3.fsf@gitster-ct.c.googlers.com/ and libgit2/libgit2#5352 (comment)

My plan is to relicense the library to be GPLv2 with a linking exception, ie. the library that libgit2 uses.

I think this should make integrating with go-git feasible. Can you confirm importing github.com/google/reftable is OK with you from a license perspective.

thanks!

[hanwen]

@mcuadros ping?