Update readme.md
Extract "testLastModifiedTime"
Add support for "opts.updateNeeded" + update readme
Add "compareSha1Digest"
Add "changed.compareMd5Digest"
Use more verbose mocha output
Add testdata files
Add tests for hash comparers
Add unit test for extension change
Update readme formatting
Standardize to using single quotes, not double
Add details about "opts.updateNeeded" to readme
Mark readme code blocks as JavaScript
Move example above custom fn description in readme

- Thanks @101100
Test both relative and absolute "dest"

- I temporarily removed "test" call with
  absolute path because it caused a merge
  conflict with #13 during rebase;
  adding it back now (with an extra test
  for absolute path with extension)
Rename "testdata" to "fixture"
Updates as per @sindresorhus review
Readme updates as per @sindresorhus review