Don't hyperlink no-color output

Before this release, piped riff output could contain OSC hyperlinks,
potentially messing up for other tools.

With this change in place, riff will not emit hyperlinks when its output
is not a terminal.

Change default unchanged style to Yellow

I believe this is much more helpful than red-green, so this will be the
new default.

To revert back to the old behavior, set...

    RIFF=--unchanged-style=red-green

... in your environment.

With this release we also drop the "experimental" unchanged style
option, which was identical to yellow. The old experimental / yellow is
the new default, and no options are needed for that any more.

Hyperlink to the right place in the files

Before this release, hunk header hyperlinks went to some lines above the
actual change.

With this release, those same hyperlinks go to the first changed line.

Hyperlink hunk headers to specific file lines

Requires moor v2.6.1 or later for the new hyperlinks to render
correctly.

Highlight rename-only diffs

Before this release, renames were only highlighted if there were
contents changes as well. With this release, "rename from" and "rename
to" lines are now highlighted even if there are no other changes.

Also, this release fixes a crash when the PAGER environment variable is
set to an empty string.

Our favorite pager was renamed, it is now `moor`

Ref: walles/moor#305

Hyperlink file names in diffs

File names mentioned in the diff can now be clicked.

Render ESC characters in the diff as Unicode ␛

This enables diffing changes to ANSI styled text files.

Don't group Hiragana / Katakana into words

It never worked.

Accept arguments in PAGER variable