Added option to use re2j for CSS query regexes

[jhy]

Added support for using the re2j regular expression engine for CSS selectors, which ensures linear-time performance for regex evaluation. This enables safe handling of arbitrary user-supplied query regexes.

To enable, add the com.google.re2j dependency to your classpath, e.g.:

<dependency>
  <groupId>com.google.re2j</groupId>
  <artifactId>re2j</artifactId>
  <version>1.8</version>
</dependency>