First release of expresso

---

It is now ca 1 month before gsoc ends. It has been a fantastic time and valuable learning experience so far!

Expressos basic functionality is now in place. It is convenient for handling expressions, can simplify/differentiate/solve/optimize them and compile them to efficient clojure functions.

Maybe there are some early adopters, who want to use expresso's symbolic manipulation and want to give it a try! (and report issues/bugs etc) See the github repository and README.md for details.