Let's acknowledge everyone's contributions by replacing "Google LLC"
in the copyright header by "The Jujutsu Authors". If I understand
correctly, it won't have any legal effect, but maybe it still helps
reduce concerns from contributors (though I haven't heard any
concerns).
Google employees can read about Google's policy at
go/releasing/contributions#copyright.
I feel the original -------/+++++++ pair is slightly confusing because
each half can be a separator by itself. I don't know what character other
than '-'/'+' is preferred, but let's pick '%' (for "mod") per @martinvonz
suggestion.
I'm adding this mostly because it's useful for testing. That's also
the reason it supports displaying conflicts. I didn't call it `cat`
like `hg cat` because I haven't found `hg cat` on multiple files
useful.
