long overdue version bump to 0.4 (highlights in extended commit message)

Highlights:
* diff granularity options
* using diff-lcs gem instead of some weird code snatched up from somewhere
  years ago
* less shite HTML output
* code stubs for testing and profiling
* at least 5x speedup!

some more cleanup, -1 from todo, VERSION: 0.3

+GPL license text