merge: add conflict marker formatter (BC)
Adds a conflict marker formatter that can produce custom conflict marker
descriptions. It can be set via ui.mergemarkertemplate. The old behavior
can be used still by setting ui.mergemarkers=basic.
The default format is similar to:
{node|short} {tag} {branch} {bookmarks} - {author}: "{desc|firstline}"
And renders as:
contextblahblah
<<<<<<< local: c7fdd7ce4652 - durham: "Fix broken stuff in my feature branch"
line from my changes
=======
line from the other changes
>>>>>>> other: a3e55d7f4d38 master - sid0: "This is a commit to master th...
morecontextblahblah
....................
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Ran 20 tests in 0.000s
OK