Merge branch 'pw/merge-tree-stdin-deadlock-fix'

"git merge-tree --stdin" has been improved (including a workaround for a deadlock). * pw/merge-tree-stdin-deadlock-fix: merge-tree: fix link formatting in html docs merge-tree: improve docs for --stdin merge-tree: only use basic merge config merge-tree: remove redundant code merge-tree --stdin: flush stdout to avoid deadlock