Update README.md

Customized readme for this project.
Update README.md

Clarified intro.
Customize project description.
- Clean-up and reorganize code for readability.
- Introduce checks to ensure that only HTML responses are modified.
Fix consistency of tabs and spaces.
Version bump.
Add a safe-guard in case content-type header is missing for some reason.
Preparing separate branch for pull request.
Add htmlOnly argument back-in to maintain compatibility for up-stream PR.
Link mime-detection behavior to whether or not htmlOnly is set.
Update test cases for new mime sniffing capability.
Fix a very subtle bug with closures and local variables that caused selectors not to apply correctly.
Fix a related subtle bug with closures that would have caused multiple requests to affect one another.
Remove excess spaces.
Fix handling of default value for htmlOnly.
Merge pull request #17 from GuyPaddock/pull_request_prep

Clean-up code for clarity / make binary-safe