Use full path for PhantomJS instead of path to parent directory

This PR changes the `path` configuration option to be the full binary path to PhantomJS instead of the parent directory. This change was first proposed in PR #7.

## Backwards Compatibility Support

Backwards compatibility is kept by checking if the path passed in through the configuration is a directory or not. If its found to be a directory, `/phantomjs` is appended to the path like it was done before.

## Readme changes

Re-formatted README to better show a customization example along with all available options that Phantoman currently supports which were added in PR #9.