McIlroy-Hunt longest common subsequence algorithm implementation

 Diff::LCS is a port of Algorithm::Diff that uses the McIlroy-Hunt
 longest common subsequence (LCS) algorithm to compute intelligent
 differences between two sequenced enumerable containers. The
 implementation is based on Mario I. Wolczko's Smalltalk version,
 and Ned Konz's Perl version (Algorithm::Diff).