add travis ci build

Hi, this pr add build file for https://travis-ci.org

build every commit is:
- compile solution
- run unit tests

Example log of this commit build: https://travis-ci.org/enricosada/ExtCore/builds/15831044
Example badge: https://github.com/enricosada/ExtCore/tree/travisbuild

let me know if you need more info about it

after merge you need to change badge url from my repo to yours