examples/diff: Add minimal, patience diff options.

- Add minimal, patience diff options to diff example. libgit2
  `diff_xdiff.git_xdiff_init` already supports these flags, so
  no additional change is necessary.
- Remove minimal and patience flag addition from project list.
Merge pull request #2160 from modocache/examples-diff-add-patience-and-minimal

examples/diff: Add minimal, patience diff options.