go library used to create, modify, and print diffs

 The top level package, diff, contains convenience functions for the most
 common uses.
 .
 The sub-packages provide very fine-grained control over every aspect:
   * myers creates diffs using the Myers diff algorithm.
   * edit contains the core diff data types.
   * ctxt provides tools to reduce the amount of context in a diff.
   * write provides routines to write diffs in standard formats.