Rename SexMachine to Gender::Detector

Hi!

I'd like to propose renaming SexMachine to Gender::Detector.

Now, I know many people wouldn't consider this the most important topic in the world, but I think that this change is something simple and easy that we Rubyists can do to become a safer, more welcoming place to women software engineers. And I know I'm not the only one that thinks so (https://github.com/bmuller/sexmachine/issues/9)

SexMachine is an overly sexual name, which does not belong in a work environment. This sexualized name can inadvertently cause women to become uncomfortable, and to feel excluded. Naming this gem SexMachine sends a message to sexist men that sexual jokes are allowed, which promotes an unhealthy atmosphere.

I know many people don't realize why some women might feel uncomfortable with the name of this gem. Unfortunately, the society we live in today is polarized around the topic of sexuality, and more importantly, who has the power with respect to sexuality. This power dynamic is heavily skewed toward male favor. Men can joke about their sexuality and this is a source of manliness and pride. A woman cannot feel free to discuss similar topics without a very real threat of being called a sexual pejorative. 

Even though this rename removes a fun play on words, I'd like to think that providing a community that shows it is welcoming to women more than outweighs this loss.
"Gender" should probably be lowercase here.