3.3.7: Enable building with older Rust versions

Enable building with older Rust versions

3.3.6: Prevent timeouts on large differences

By not doing any refinement on the large sections.

3.3.5: Improved conflicts highlighting + highlighting TNG

With this release, many more conflicts are recognized, and changes vs
non-changed line parts are marked much more clearly.

Also, this release introduces a --unchanged-style=experimental
command line option. Try export RIFF=--unchanged-style=experimental
and report back!

3.3.4: Tune conflicts highlighting

Both by clearly highlighting the markers, and by improving how we color
the conflicting areas themselves.

And remember: "git config --global merge.conflictstyle diff3" is your
friend!

3.3.3: Further improve what we highlight and not

With this release, we go from plain LCS to the Patience Diff algorithm.
"Patience" is marketed as producing more human friendly diffs.

Additionally, post processing has been tuned to take better decisions on
which differences should be highlighted and not.

3.3.2: Tune what gets highlighted and not

Tune what gets highlighted and not

3.3.1: Tune leading whitespace lowlighting

We should always have lowlighted leading whitespace for both old and new
lines, but that was forgotten about.

This release fixes that.

Also, some tuning was done on when we should / should not highlight
changes.

3.3.0: Don't highlight leading whitespace

I think diffs look better this way.

But in general I feel that I usually don't care about whitespace changes,
so highlighting those makes no sense.

I also looked at my examples in the testdata directory and concluded
that the examples that changed looked better now.

3.2.1: Tune file name rendering

Before this release, file names were rendered in all bold.

Starting with this release though, the paths are rendered in normal intensity,
but the actual file names are kept bold.

The goal of this is to improve readability of the output.

3.2.0: Improved conflicts highlighting

Especially for diff3 conflicts, where we now show unchanged lines vs base in context color:
https://stackoverflow.com/questions/27417656/should-diff3-be-default-conflictstyle-on-git

With this release, we are also better at detecting conflict markers in git diff output.