Update Data.Algorithm.Diff to Diff-0.3.0

Changes: deletions listed before insertions, new constructors.
Change diff output to unidiff format

This format is the output of `diff -u`, with a two-line header, hunk
headers with ranges, and context lines. It's also the format used by
`patch` and `git diff`, so it should be more useful and familiar to
programmers.
Move ColourDiff to Aura.Diff

ColourDiff depends on Aura.Colour.Text, so it doesn't make sense for
it to be outside the Aura directory.
Use new diff format

Headers are "a/pkgname/PKGBUILD" and "b/pkgname/PKGBUILD".
Merge pull request #134 from knrafto/diff

Change diff output to that of `diff -u` or `git diff`