General clean up

I've done some general changes, nothing should break backwards compatibility and a new release shouldn't be necessary, these are the changes;

- Added .DS_Store to .gitignore
- Converted tabs to spaces
- Converted two spaces to four spaces
- Added watch task to grunt file
- Expanded example code
- Converted API methods in read me to headings
- Removed readMeFilename and gitHead from package.json as it's non-standard see https://github.com/isaacs/npm/issues/3573#issuecomment-19550501
- Added contributors to package.json
- Moved source files to src, compiled files to dist, documentation/website file to docs
- Changed main in grunt file to src/ssm.js see https://npmjs.org/doc/json.html#main