Add CI for smoke testing

[nturley]

discussed in #104, we should add continuous integration to fusesoc. There's different levels of testing that could be added, but this specific issue only tracks basic smoke testing

CI should install and execute init, list-cores, list-systems, and update
CI should get OS coverage on a linux system and a windows system.
CI should test multiple versions of python on each OS. Python 2.7 and 3.5 at minimum.

[olofk]

Thanks for the patches. Tests are successfully running with both Travis and Appveyor now