plumbing: commit.StatsContext and fix for orphan commit (src-d#1115)

plumbing: commit.StatsContext and fix for root commit

Merge pull request src-d#1065 from vmarkovtsev/fix-unicode

Remove Unicode normalization in difftree

Merge pull request src-d#1056 from jfontan/fix/lose-objects-shared-cache

storage/filesystem: check file object before using cache

Merge pull request src-d#1045 from kuba--/enh-1024/log-all

Implement git log --all

Merge pull request src-d#1028 from smola/clone-regression

repository: fix plain clone error handling regression

Merge pull request src-d#1025 from mcuadros/eoie

plumbing: format/index: support for EOIE extension

Merge pull request src-d#985 from mcuadros/checkout-doc

repository: improve CheckoutOption.Hash doc

worktree: solve merge conflicts

Merge pull request src-d#920 from vancluever/f-add-commit-signkey

git: Add ability to PGP sign commits

Merge pull request src-d#874 from smola/patchcontext

plumbing: add context to allow cancel on diff/patch computing