Compare Two Commits

Produces a raw git-style diff.#### Single commit specIf the `spec` argument to this API is a single commit, the diff isproduced against the first parent of the specified commit.#### Two commit specTwo commits separated by `..` may be provided as the `spec`, e.g.,`3a8b42..9ff173`. When two commits are provided and the `topic` queryparameter is true, this API produces a 2-way three dot diff.This is the diff between source commit and the merge base...