Output type for Vectorized h3.geo_to_h3()

[Anubis-Jackal]

Hi, when I was using the vect.geo_to_h3() function under h3.unstable that was introduced in #147, I seem to get results as uint64 as opposed to the expected hex string representation. I was wondering if there was a way to convert the output formats while maintaining the speed of this vectorized function. There doesn't seem to be a vectorized version of h3_to_string, which would serve my purpose well. Huge thanks to @ajfriend for creating this tool!