Log Message:
textproc/diffr: import package

Reviewing changes involves reading diffs. Sometimes, a line-oriented
presentation of changes is not precise enough, especially when changes
involve long lines or very similar consecutive lines.

This program processes such diffs, and output them (in the console)
with additional diff information on top of the unified diff format,
using text attributes.

It works hunk by hunk, recomputing the diff on a word-by-word basis.