Add testing

[hakonanes]

Oh boy, we cannot wait too long before writing tests for it all. Shouldn't be too much work if we just look at what pyXem and HyperSpy does.

[hakonanes]

With pytests as HyperSpy and pyXem does it, also setting up Coveralls and Travis CI.

[hakonanes]

TravisCi is now set up, need to:

• [x] Setup pytest and start writing tests
• [x] Change TravisCI configuration (yaml) file to do testing in after_install part
• Write tests for it all...

[hakonanes]

TravisCI (https://travis-ci.org/kikuchipy/kikuchipy) and Coveralls (https://coveralls.io/github/kikuchipy/kikuchipy) is now set up.