I'm interested in exploring a career in mobile web development. I know bits and pieces of html, css, javascript, and php.If you were to advise someone in my position, what language (or stacks) would you advise me to really get proficient in? What language is hot? What language will stick around and evolve? I dont want to spend a lot of time learning something that's not going to be around for long. Someone told me that Ruby On Rails is hot. What do you guys think? THanks.